#algos-and-data-structs | Python | Page 19

fiery cosmos Nov 7, 2022, 12:53 AM

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i am not

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im just wondering about the asymptotics of if i were

haughty mountain Nov 7, 2022, 12:53 AM

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for a list no

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if you delete in the middle of a list you need to shift all the element right of it one step left

fiery cosmos Nov 7, 2022, 12:53 AM

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ahh ok

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ooh i just thought of some great analysis to write about

haughty mountain Nov 7, 2022, 12:55 AM

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linked list -> O(n) indexing, O(1) removal if you're "at" the index
list -> O(1) indexing, O(n) removal

fiery cosmos Nov 7, 2022, 12:55 AM

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oh they're reversed

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interesting

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ditto for inserting, O(1) for linked, O(n) for normal list, because of the shifting ducky_australia

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alright but i really must go now, tysm!!!

haughty mountain Nov 7, 2022, 1:02 AM

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as I mentioned, O(1) insertion is only true for linked list if you insert at a node you already have O(1) access to

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and I suspect deque doesn't even have O(1) insertion in the middle anyway, even if it was a supported operation like in usual linked lists

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deque is a linked list of blocks, and I expect it will "re-align" the blocks on insertion/deletion

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I haven't checked the source though

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but in short just use deque for deque operations, most other operations are terrible

opal oriole Nov 7, 2022, 1:09 AM

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Unrolled doubly linked list I think.

haughty mountain Nov 7, 2022, 1:22 AM

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it's a kinda worse version of C++'s deque

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which has O(1) indexing

opal oriole Nov 7, 2022, 1:29 AM

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More memory, but if you want that O(1), worth.

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(Can use the technique in general on linked lists / unrolled linked lists)

gleaming pivot Nov 7, 2022, 4:49 AM

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class Solution(object):
    def plusOne(self, digits):
        lis = []
        for i in digits:
            if i == 9:
                return [1,0]
            elif i != 9:
                lis.append[i]
                return lis[::-1] + 1

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is it possible to solve this problem

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this method?

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https://leetcode.com/problems/plus-one/

Level up your coding skills and quickly land a job. This is the best place to expand your knowledge and get prepared for your next interview.

amber harbor Nov 7, 2022, 7:54 AM

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Hey so I'm learning about shell sort and we have to find the worst case for it. We're using the original sequence and after running the algorithm with reversed and random input, we found the random input takes more time to run. Anyone have any ideas on this? Thanks

hollow needle Nov 7, 2022, 9:08 AM

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Hello
How can you calculate epochs of Adaline algorithm with a certain epsilons and learning rate for patterns like OR ?!

haughty mountain Nov 7, 2022, 10:05 AM

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amber harbor Hey so I'm learning about shell sort and we have to find the worst case for it. ...

shell sort with gaps 1, 2, 4, 8, 16, ...?

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iirc a power of two array size is a bad case there

amber harbor Nov 7, 2022, 10:06 AM

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yup.

floral wasp Nov 7, 2022, 10:07 AM

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Hi guys, i need help i don't know how to use str on my poo look

hybrid epoch Nov 7, 2022, 10:07 AM

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gleaming pivot this method?

No. The .append method is not subscriptable. Your code returns an early, incorrect output for the input [9,9]. Also, you're trying to concatenate an int with a list

floral wasp Nov 7, 2022, 10:07 AM

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rn_image_picker_lib_temp_1059eae4-ef5c-41a5-ab62-f172e6ef1cc4.jpg

amber harbor Nov 7, 2022, 10:08 AM

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haughty mountain iirc a power of two array size is a bad case there

a power of 2 array?

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you mean like 1 2 4 8 16 32...

haughty mountain Nov 7, 2022, 10:09 AM

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amber harbor you mean like 1 2 4 8 16 32...

no, power of two long

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see https://en.wikipedia.org/wiki/Shellsort#Gap_sequences

Shellsort

Shellsort, also known as Shell sort or Shell's method, is an in-place comparison sort. It can be seen as either a generalization of sorting by exchange (bubble sort) or sorting by insertion (insertion sort). The method starts by sorting pairs of elements far apart from each other, then progressively reducing the gap between elements to be compar...

amber harbor Nov 7, 2022, 10:09 AM

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oh, I mean what data order would result in its worst case

haughty mountain Nov 7, 2022, 10:09 AM

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it mentions a worst case under the table in this section

amber harbor Nov 7, 2022, 10:09 AM

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like its best case is when the array is already sorted right?

haughty mountain Nov 7, 2022, 10:10 AM

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probably

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power of two is the worst case for the N, because consecutive zeroes

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and then that even/odd config

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so something like

n = 2**12
A = [None]*n
A[::2] = range(0, n//2)
A[1::2] = range(n//2, n)

shell_sort(A)

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not a huge case, but you can raise that power

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a few more powers up things should get pretty slow if it behaves quadratically

amber harbor Nov 7, 2022, 10:20 AM

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What is N in the example above? the number of elements in array a?

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I still don't understand it very well... could you perhaps give me an example?

haughty mountain Nov 7, 2022, 11:06 AM

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amber harbor What is N in the example above? the number of elements in array a?

!e yes, n is the number of elements of A

n = 2**4
A = [None]*n
A[::2] = range(0, n//2)
A[1::2] = range(n//2, n)

print(A)

halcyon plankBOT Nov 7, 2022, 11:06 AM

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@haughty mountain :white_check_mark: Your 3.11 eval job has completed with return code 0.

[0, 8, 1, 9, 2, 10, 3, 11, 4, 12, 5, 13, 6, 14, 7, 15]

haughty mountain Nov 7, 2022, 11:06 AM

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so small/large elements on even/odd positions respectively

amber harbor Nov 7, 2022, 11:08 AM

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haughty mountain so small/large elements on even/odd positions respectively

so like, 1000, 3, 9889, 34, 1485, 9, 438, 9...

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like that?

haughty mountain Nov 7, 2022, 11:09 AM

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you can see the example I gave

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positions 0, 2, 4, ... have elements 0, ..., n-1

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positions 1, 3, 5, ... have elements n, ..., 2n-1

amber harbor Nov 7, 2022, 12:36 PM

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oh... I see. thank you

lucid wyvern Nov 7, 2022, 3:26 PM

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Hey is this where I can ask help to optimise a program ?

agile sundial Nov 7, 2022, 3:27 PM

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probably

lucid wyvern Nov 7, 2022, 3:29 PM

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TLDR a group of friend and I are trying to get the number than appear more than 3 times in the inner triangle of a pascal triangle as fast as possible.
We've set up the limit row to 250

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And so far I'm here :

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def search_pascal_multiples_fast(row_limit):
    triangle = [[1]]
    for i in range(row_limit):
        triangle.append([1] + [triangle[i][j-1] + triangle[i][j] for j in range(1, len(triangle[i]))] + [1])
    return sorted([number for number, count in Counter([number for row in [row[1:-2] for row in triangle] for number in row]).items() if count > 3])

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And I clueless on how to make it better. Any ideas ?

vocal gorge Nov 7, 2022, 4:21 PM

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huh, interesting. what comes to my mind is what it means mathematically: e.g. 120 occurs in 5 places because binomial(10,3)=binomial(10,7)=binomial(16,2)=binomial(16,14)=binomial(120,1). That last one is always going to be there and the first four are two pairs. So what's special about 120 is just that it happens that

10!/(3! 7!) = 120 = 16!/(2! 14!)

which... doesn't give me any fancy ideas on how to predict it, hmm.
Of course, OEIS has an entry for it, https://oeis.org/A003015, and it's 20 years old and has tons of references. But it seems like it really is just a search task.

lucid wyvern Nov 7, 2022, 4:29 PM

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Yeah but most of maths concept they mention here fly right over my head.
The only one I have a grasp on is the nCr and it's slower than my approach

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But I did try singmaster's conjecture

fiery cosmos Nov 7, 2022, 4:46 PM

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hey all, i need help implementing a randomized list for my algo. i don't want it to be truly random, so i'll need random seed i think. what i would like to do is, if the range i say (0-10), put the numbers in the same random order each time i run the program. i cannot pre-determine the random stack because it'll vary in size.

lucid wyvern Nov 7, 2022, 4:47 PM

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fiery cosmos hey all, i need help implementing a randomized list for my algo. i don't want it...

Random.seed(Random.randomint(1,10))?

fiery cosmos Nov 7, 2022, 4:48 PM

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ok i will try this, thank you

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do i need like a i for i in random.seed...

lucid wyvern Nov 7, 2022, 4:54 PM

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Random.seed() takes an integer so what I wrote previously should work I think

fiery cosmos Nov 7, 2022, 4:55 PM

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no you have to set the seed somehow, will google

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ty

lucid wyvern Nov 7, 2022, 4:55 PM

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fiery cosmos no you have to set the seed somehow, will google

Yes with the random.randint(1,10)

fiery cosmos Nov 7, 2022, 4:56 PM

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then you would be randomizing the seed to one of those

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the seed confers a non-randomness to the random function, or at least, the same "randomness" each time

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import random

random.seed(1)

list = [i for i in (random.randint(0,10))]

print(list)

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this gives error:

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Exception has occurred: TypeError 'int' object is not iterable

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so i'll need a range somewhere as well

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ah, randrange

midnight sorrel Nov 7, 2022, 5:05 PM

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Hi, I have a binary matrix of size o*p. I'm given K queries where each consists of given sub-matrix, with upper left coord (x1,y1) and lower right coord (x2,y2).
My task is to count one's in each submatrix. It should be done in O(o*p + k) time complexity. How do I do that?

fiery cosmos Nov 7, 2022, 5:37 PM

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hey all, i need to update some logic for my hashtable

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lmk if you can assist

fiery cosmos Nov 7, 2022, 6:41 PM

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i was trying to randomize a list in the same way each time, but i've abandoned that. now i am trying to fix up my logic for when i pick a new bucket to place a key into. its a hashtable algo

fiery cosmos Nov 7, 2022, 6:41 PM

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fiery cosmos ah, `randrange`

.

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i'm struggling with my logic bc i essentially have like a while trying and failing thing is true: do x but i'm not able to see how to meet the original condition to break the while look

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loop

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i'm ending up just inserting the same key over and over again

vocal gorge Nov 7, 2022, 6:55 PM

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midnight sorrel Hi, I have a binary matrix of size o\*p. I'm given K queries where each consists...

Hint: consider a lower-dimensional version of this: you have an n-sized array, and you are asked to quickly (O(1) per query, after O(n) preparation) answer queries of the form "what's the sum of elements a[i]+a[i+1] + ... + a[j-1]?" (so, the sum of a[i:j]). Do you know how to solve this one?

haughty mountain Nov 7, 2022, 6:56 PM

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fiery cosmos ```py import random random.seed(1) list = [i for i in (random.randint(0,10))] ...

[randint(...) for _ in range(n)]

fiery cosmos Nov 7, 2022, 7:00 PM

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its a bit more nuanced, i need them to be unique. but i'm more focused rn on trying to implement the logic you mentioned y'day, eg, while failing a try_insert, pick new bucket location, try again. i am going to read over the old messages now

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lol i just end up inserting the same key for every location in the table

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ok i think i got it

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wait, nvm

opal oriole Nov 7, 2022, 7:09 PM

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https://docs.python.org/3/library/random.html#random.sample

fiery cosmos Nov 7, 2022, 7:12 PM

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i got it inserting and not overwriting anything but now i am unable to insert all of my keys and i'm not sure why

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i have plenty of space in the table

fiery cosmos Nov 7, 2022, 7:12 PM

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opal oriole https://docs.python.org/3/library/random.html#random.sample

oh, this gives uniqueness. thank you

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this is exactly what i wanted thanks. this works:
self.stack = random.sample(range(0,primary_hash_int),primary_hash_int)

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something about my chaining logic is still broken

fiery cosmos Nov 7, 2022, 7:30 PM

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fiery cosmos this is exactly what i wanted thanks. this works: `self.stack = random.sample(ra...

can i use a random seed so that the sampling will be the same each time for a given primary hash variable?

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yep

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awesome

opal oriole Nov 7, 2022, 7:32 PM

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https://docs.python.org/3/library/random.html#random.seed

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(random.seed(0) or whatever)

fiery cosmos Nov 7, 2022, 7:32 PM

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yep. i got it. tested and everything

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pretty neat

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reproducible randomness

opal oriole Nov 7, 2022, 7:35 PM

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(For reference: https://en.wikipedia.org/wiki/Fisher–Yates_shuffle, non-inplace version uses a hashmap to keep track of swaps)

fiery cosmos Nov 7, 2022, 7:36 PM

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dude, Knuth is everywhere in this field

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thanks for ref

opal oriole Nov 7, 2022, 7:37 PM

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Knuth might as well be the field.

fiery cosmos Nov 7, 2022, 7:37 PM

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i swear everywhere i look i see his name. wild the influence he has had

opal oriole Nov 7, 2022, 7:38 PM

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Knuth also just wrote a lot of notes on various things that are useful and many use them as reference.

fiery cosmos Nov 7, 2022, 7:38 PM

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i like how in the fisher-yates wiki they have a pencil and paper method

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nice way to learn an algo

opal oriole Nov 7, 2022, 7:39 PM

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Random shuffles were done on paper long before (modern) computers.

fiery cosmos Nov 7, 2022, 7:40 PM

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oh i'm sure

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i wonder how these graphs are generated not that but what dataset they're basing this on

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obviously its not search engine stuff

opal oriole Nov 7, 2022, 7:41 PM

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Book/paper references to the word.

fiery cosmos Nov 7, 2022, 7:41 PM

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right

opal oriole Nov 7, 2022, 7:41 PM

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Of all books we have.

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Google scanned in a lot of books and papers that were physical.

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But other organizations did too.

fiery cosmos Nov 7, 2022, 7:41 PM

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and sent them to Alphabet/GOOG?

opal oriole Nov 7, 2022, 7:41 PM

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Made a specific machine for it.

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But that graph looks like it's only for recent.

fiery cosmos Nov 7, 2022, 7:43 PM

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only really post 1950, or the y axis doesn't allow one to see few mentions on the scope of millions

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or whatever the upper bound is

opal oriole Nov 7, 2022, 7:44 PM

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Looks like it's per year, not cumulative, but there was a lot of "algorithm" prior 1950.

fiery cosmos Nov 7, 2022, 7:45 PM

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right im thinking we just cannot see the 1-1000 refs / year or whatever it was due to the scale of y

opal oriole Nov 7, 2022, 7:46 PM

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More than 1000.

flat hornet Nov 7, 2022, 7:46 PM

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Guys, what is the best place to learn and to train algorithms and data structurs?

fiery cosmos Nov 7, 2022, 7:46 PM

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see pins and also abdul bari on youtube

haughty mountain Nov 7, 2022, 7:46 PM

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opal oriole Knuth also just wrote a lot of notes on various things that are useful and many ...

in TeX, which he wrote

opal oriole Nov 7, 2022, 7:46 PM

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flat hornet Guys, what is the best place to learn and to train algorithms and data structurs...

Here 🙂

fiery cosmos Nov 7, 2022, 7:47 PM

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and here

flat hornet Nov 7, 2022, 7:47 PM

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learn data structurs is know how things work like in the array for example?

fiery cosmos Nov 7, 2022, 7:48 PM

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opal oriole Nov 7, 2022, 7:48 PM

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haughty mountain in TeX, which he wrote

I thought the reply was to something else.

fiery cosmos Nov 7, 2022, 7:48 PM

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also, depth first and breadth first searches

opal oriole Nov 7, 2022, 7:49 PM

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Yeah, Knuth is something else.

flat hornet Nov 7, 2022, 7:49 PM

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know the performance of components, what is better for use?

fiery cosmos Nov 7, 2022, 7:49 PM

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heaps

flat hornet Nov 7, 2022, 7:49 PM

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fiery cosmos

this is main types of data struturs?

fiery cosmos Nov 7, 2022, 7:50 PM

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those are some common ones, they you have the ways you want to represent your graphs, you have the graph traversal algorithms, there are heaps, etc

haughty mountain Nov 7, 2022, 7:50 PM

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opal oriole I thought the reply was to something else.

I'm just saying he made TeX to typeset his things 🙂

fiery cosmos Nov 7, 2022, 7:50 PM

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kind of mixing in DS and different algos here, but each algorithm is underpinned by one or more datastructure

fiery cosmos Nov 7, 2022, 7:51 PM

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flat hornet this is main types of data struturs?

https://www.bigocheatsheet.com/

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the stack and queue mentioned there can be implemented as a pythonic array or deque

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fiery i hate to ask but are you able to assist with fixing my chaining logic

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i have it running but i am failing to insert all of my keys

haughty mountain Nov 7, 2022, 7:57 PM

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why is there an else there?

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up top

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ok, why is your else doing all that?

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why are there try_inserts in the else?

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the else is only there to deal with linking a new bucket

flat hornet Nov 7, 2022, 7:59 PM

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do you need make functions

fiery cosmos Nov 7, 2022, 7:59 PM

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haughty mountain the else is only there to deal with linking a new bucket

🤔

fiery cosmos Nov 7, 2022, 7:59 PM

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flat hornet do you need make functions

you're not seeing the entire prog

haughty mountain Nov 7, 2022, 8:00 PM

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y'know, you might benefit from adding a comment to each block to remember what it's supposed to do, which might deter you from making it do something it shouldn't do

fiery cosmos Nov 7, 2022, 8:01 PM

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you aren't wrong, i need to do that anyway before submission

haughty mountain Nov 7, 2022, 8:02 PM

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you still need the while loop if you're going with the "potential free list" route

fiery cosmos Nov 7, 2022, 8:03 PM

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how about this:

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no i need my try except block

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i keep getting pop from empty list errors

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or maybe just a break

haughty mountain Nov 7, 2022, 8:04 PM

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yep, I would move the keys[0] is not None into a method in the Bucket though

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e.g. is_empty

fiery cosmos Nov 7, 2022, 8:05 PM

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ok ok

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wait

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i don't need that bucket argument

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this is a bucket

haughty mountain Nov 7, 2022, 8:06 PM

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while self.stack and ...:
  ...
if not self.stack:
  raise ...exception about no free buckets...

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return self.keys[0] is None

fiery cosmos Nov 7, 2022, 8:14 PM

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so i should not have any try_inserts in my else block at all?

haughty mountain Nov 7, 2022, 8:15 PM

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fiery cosmos so i should not have any `try_inserts` in my else block at all?

why would you?

fiery cosmos Nov 7, 2022, 8:16 PM

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in the event that the insert is successful, i want to update the pointers

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err

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the is_empty method will guarantee successful insertion

haughty mountain Nov 7, 2022, 8:17 PM

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if you want to add a comment to that block it would be like

# Add a new bucket to chain

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as the comment suggests, no insertion is going on

haughty mountain Nov 7, 2022, 8:18 PM

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fiery cosmos in the event that the insert is successful, i want to update the pointers

you are in the else case, so you know you have to link a bucket

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so find a free bucket, link it, and go to that bucket

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yeah, you also need one of the pops before

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well

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you could also do a different style loop I guess

fiery cosmos Nov 7, 2022, 8:21 PM

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no matter the logic i continuously find i am unable to add all keys

fiery cosmos Nov 7, 2022, 8:23 PM

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haughty mountain `return self.keys[0] is None`

for which return here

haughty mountain Nov 7, 2022, 8:23 PM

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this is iffy but should work

while True:
  if not self.stack:
    raise ...
  new_p = self.stack.pop()
  if ...[new_p].is_empty():
    break

haughty mountain Nov 7, 2022, 8:24 PM

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fiery cosmos for which return here

it's the whole function body

fiery cosmos Nov 7, 2022, 8:25 PM

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haughty mountain this is iffy but should work ```py while True: if not self.stack: raise .....

what about the pointer updates

haughty mountain Nov 7, 2022, 8:26 PM

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just do it afterwards?

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the loop is to find a free bucket

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when you have that you know what to do

fiery cosmos Nov 7, 2022, 8:26 PM

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ah ok

haughty mountain Nov 7, 2022, 8:27 PM

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again, a reasonable place to add a comment

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for the loop

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that it finds a free bucket

fiery cosmos Nov 7, 2022, 8:29 PM

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hmm im struggling with the whole passing along new_p vs the original p thing

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like i can't just name it p or it'll overwrite where i want to put the pointer

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i guess this is where i need that logic i pasted above

haughty mountain Nov 7, 2022, 8:29 PM

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the bottom two lines

fiery cosmos Nov 7, 2022, 8:30 PM

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yeah i got it

haughty mountain Nov 7, 2022, 8:30 PM

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update the link, then follow the link

fiery cosmos Nov 7, 2022, 8:30 PM

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ugh it's just adding the same keys over and over

haughty mountain Nov 7, 2022, 8:30 PM

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huh?

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code?

agile sundial Nov 7, 2022, 8:31 PM

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raising the string is wild

haughty mountain Nov 7, 2022, 8:31 PM

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yeah, raise your custom exception

fiery cosmos Nov 7, 2022, 8:31 PM

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no i know i can fix that later

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we did a lot of error handling yesterday

haughty mountain Nov 7, 2022, 8:32 PM

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what's the rest of the loop?

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lol

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yeah, no wonder

fiery cosmos Nov 7, 2022, 8:33 PM

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😢

haughty mountain Nov 7, 2022, 8:34 PM

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let's think, how can multiple of the same key even be inserted?

fiery cosmos Nov 7, 2022, 8:34 PM

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why do i feel like the culprit is my second try_insert call in elif

fiery cosmos Nov 7, 2022, 8:35 PM

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haughty mountain let's think, how can multiple of the same key even be inserted?

if it inserts and follows a pointer and inserts the same key again for a given i

haughty mountain Nov 7, 2022, 8:35 PM

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wait, why do you have an try_insert there?

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it's an error

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but not the error I saw

fiery cosmos Nov 7, 2022, 8:35 PM

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how else might i try to insert after following the pointer?

haughty mountain Nov 7, 2022, 8:37 PM

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fiery cosmos how else might i try to insert after following the pointer?

again, you wouldn't make these mistakes if you would have added comments about the steps you're supposed to do

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the last step doesn't need insert anything

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it just adds a bucket and moves to it

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the second step (in the elif) should similarly not insert

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it does a way simpler task

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elif there is a link:
  ???

fiery cosmos Nov 7, 2022, 8:42 PM

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ok let me ask you this, how can we spend multiple iterations of i to insert a single element

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we'd run out of loop iterations to insert them all, or could potentially

haughty mountain Nov 7, 2022, 8:43 PM

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fiery cosmos ok let me ask you this, how can we spend multiple iterations of i to insert a si...

you could write it as a while loop, I think you opted for the for loop way back

fiery cosmos Nov 7, 2022, 8:43 PM

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if we spend several loops to find the proper p value, we've used multiple of our finite number of loops to insert one key

haughty mountain Nov 7, 2022, 8:44 PM

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so?

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the reason we have n iterations is that it's for sure enough iterations

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it's effectively a while loop

fiery cosmos Nov 7, 2022, 8:45 PM

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i don't believe it is. it's only enough if we are guaranteed to insert the key during a single iteration. consider when keys = tablesize

haughty mountain Nov 7, 2022, 8:45 PM

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err

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this loop is for inserting 1 key

fiery cosmos Nov 7, 2022, 8:46 PM

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correct

haughty mountain Nov 7, 2022, 8:46 PM

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ok, what's the issue?

fiery cosmos Nov 7, 2022, 8:47 PM

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if we fail our first insert, and never attempt another one, we're using at least 2 of the tablesize number of iterations to insert a single key

haughty mountain Nov 7, 2022, 8:48 PM

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fiery cosmos if we fail our first insert, and never attempt another one, we're using at least...

so? it's not like we have tablesize iterations to insert a bunch of keys

fiery cosmos Nov 7, 2022, 8:49 PM

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hmm this might explain why i had it working before but i was failing to insert all the keys

haughty mountain Nov 7, 2022, 8:49 PM

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this loop is to insert a single key

fiery cosmos Nov 7, 2022, 8:50 PM

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right, but its not guaranteed to. what if we use 5 of our tablesize iterations to insert 1 key, and each key takes > 1 iteration to insert on average? we would run out of iterations

haughty mountain Nov 7, 2022, 8:50 PM

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wdym?

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how would we run out of iterations?

fiery cosmos Nov 7, 2022, 8:51 PM

#

if we are not inserting during any given iteration, only finding a new p, we could run out of iterations to insert every key, especially as the number of keys to insert gets closer to the tablesize

#

shit i really wish i could go back to what i had before and test with a larger bound on the loop..

haughty mountain Nov 7, 2022, 8:52 PM

#

err, let's fix the loop first and then come back to this

#

did you fix the elif?

fiery cosmos Nov 7, 2022, 8:52 PM

#

fair enough. but i hope you can tell what i'm on about. i removed the try_insert from there

haughty mountain Nov 7, 2022, 8:53 PM

#

haughty mountain ``` elif there is a link: ??? ```

fill in the blank in the pseudocode

fiery cosmos Nov 7, 2022, 8:53 PM

#

haughty mountain ``` elif there is a link: ??? ```

set p equal to the link pointer value

haughty mountain Nov 7, 2022, 8:53 PM

#

i.e. follow the link

#

ok, there is a very simple reason why your code inserts the same key over and over

flat hornet Nov 7, 2022, 8:54 PM

#

where is apply data structurs in python, in what functions?

haughty mountain Nov 7, 2022, 8:54 PM

#

look at your if block

fiery cosmos Nov 7, 2022, 8:57 PM

#

need a break?

haughty mountain Nov 7, 2022, 8:57 PM

#

I'll take a break

fiery cosmos Nov 7, 2022, 8:57 PM

#

lol

haughty mountain Nov 7, 2022, 8:58 PM

#

yes, you successfully inserted

fiery cosmos Nov 7, 2022, 8:58 PM

#

ok so that's much better, now im only failing to insert 3 keys

haughty mountain Nov 7, 2022, 8:58 PM

#

you're done, so break or even return

#

could you post the full loop?

#

just to check it looks alright now

#

yeah, that looks fine

fiery cosmos Nov 7, 2022, 9:00 PM

#

btw i randomized the stack with a seed for better performance 🙂

#

ok yeah it is somewhat surprising i am failing to insert every key

haughty mountain Nov 7, 2022, 9:00 PM

#

fiery cosmos fair enough. but i hope you can tell what i'm on about. i removed the try_insert...

let's get back to this

#

so what's the issue you're seeing?

fiery cosmos Nov 7, 2022, 9:01 PM

#

yeah no nvm. i was thinking this whole loop was to insert every key. nevermind

#

i was incorrect

haughty mountain Nov 7, 2022, 9:01 PM

#

fiery cosmos yeah no nvm. i was thinking this whole loop was to insert every key. nevermind

I repeatedly said "the loop is to insert a single key" 😛

fiery cosmos Nov 7, 2022, 9:01 PM

#

i know i know

#

it just clicked

haughty mountain Nov 7, 2022, 9:02 PM

#

and why is n steps enough?

fiery cosmos Nov 7, 2022, 9:02 PM

#

uh

#

i suppose in the condition that every single other table slot is full?

haughty mountain Nov 7, 2022, 9:03 PM

#

how many unique links can you even follow in a row?

fiery cosmos Nov 7, 2022, 9:03 PM

#

in the unlikely condition that every try_insert fails

haughty mountain Nov 7, 2022, 9:03 PM

#

how many links are there?

fiery cosmos Nov 7, 2022, 9:03 PM

#

oh idk

haughty mountain Nov 7, 2022, 9:04 PM

#

there are only n links

fiery cosmos Nov 7, 2022, 9:04 PM

#

n-1

haughty mountain Nov 7, 2022, 9:04 PM

#

right

#

you'll never be able to follow n links

fiery cosmos Nov 7, 2022, 9:05 PM

#

ok sweet. any idea why i'm failing to insert some? i should try a larger input too.

#

rn keys = 84

#

when tablesize is 120, and input keys = 115, i successfully add 106 keys and fail to insert 9

#

seems to be some constant fraction of the keys

#

interesting

#

https://tenor.com/view/curious-genius-magic-harry-potter-wand-gif-5016321

Tenor

haughty mountain Nov 7, 2022, 9:06 PM

#

I'm assuming you meant to call is_empty

fiery cosmos Nov 7, 2022, 9:07 PM

#

where

haughty mountain Nov 7, 2022, 9:07 PM

#

in the code I replied to

#

it's only used once

fiery cosmos Nov 7, 2022, 9:09 PM

#

uhh, you want it in elif? eg, elif table p has a pointer, follow it and check if that slot is empty?

haughty mountain Nov 7, 2022, 9:09 PM

#

you're not calling the is_empty function in your code

fiery cosmos Nov 7, 2022, 9:10 PM

#

its in the else clause, do i need it more than that?

haughty mountain Nov 7, 2022, 9:10 PM

#

...call it

fiery cosmos Nov 7, 2022, 9:11 PM

#

oooooooooo

haughty mountain Nov 7, 2022, 9:11 PM

#

thanks lancebot

fiery cosmos Nov 7, 2022, 9:11 PM

#

ty

#

yep, that fixed it up

#

ty ty

#

ok, i think i am finally done tinkering and ready to complete the analysis. the rough part is, i need to redo every single test call and generate new numbers. i should really get busy on that bc the first time around it took me foreverrr

haughty mountain Nov 7, 2022, 9:13 PM

#

a statically typed language would have screamed at you, sadly this is python 😛

fiery cosmos Nov 7, 2022, 9:13 PM

#

i have missed those () before, yeah

haughty mountain Nov 7, 2022, 9:13 PM

#

fiery cosmos ok, i think i am finally done tinkering and ready to complete the analysis. the ...

automate the boring stuff with python

fiery cosmos Nov 7, 2022, 9:14 PM

#

you just read my mind, i had already typed out a message saying if i had more time i would write a method to run all the tests for me

#

i have 11 schemes at least, before i get into looking at the same scheme with changing input size

haughty mountain Nov 7, 2022, 9:15 PM

#

the automation shouldn't be too hard

#

you would probably save time

fiery cosmos Nov 7, 2022, 9:15 PM

#

eh, i'm sure its pretty tough given i have so many varying command line calls and different input files

haughty mountain Nov 7, 2022, 9:15 PM

#

or at least save annoyance

#

even bash would do fine

#

just a bunch of nested loops

fiery cosmos Nov 7, 2022, 9:16 PM

#

i should have made it do that automatically..

#

right now i am manually keying in each combination each time along with the arguments 🤦‍♂️

#

🤦‍♂️ 🤦‍♂️ 🤦‍♂️

haughty mountain Nov 7, 2022, 9:18 PM

#

even if you don't want the loops and that complexity

#

why not just write all the commands to run to a file?

#

and then run that

fiery cosmos Nov 7, 2022, 9:19 PM

#

wdym

haughty mountain Nov 7, 2022, 9:19 PM

#

you know the commands you type out over and over? write them one per line in a file

#

and then you can just run that file as a script

fiery cosmos Nov 7, 2022, 9:20 PM

#

how so

#

so thankfully i already have all the names, cause i have them as outputfile names

haughty mountain Nov 7, 2022, 9:21 PM

#

u0_a258: ~
> cat a.sh
echo do a
echo do b
echo do c
u0_a258: ~
> bash a.sh
do a
do b
do c

#

I'm saying write the commands to run to a file, then you can just run all in one batch

#

some manual work and copy pasting, then you can re-run stuff as needed easily

#

without typing stuff

#

(and you can avoid a ton of the initial typing using loops, but even without that this is a better way than writing everything every time)

fiery cosmos Nov 7, 2022, 9:27 PM

#

im with you. i do need to learn bash soon

haughty mountain Nov 7, 2022, 9:28 PM

#

as said, you can literally just write out the commands one per line to a file

#

that's a valid script

#

then you can run it and have everything generated by executing one script

#

suddenly the annoying part isn't annoying anymore and you don't need to fear having to redo it

fiery cosmos Nov 7, 2022, 9:30 PM

#

oh

haughty mountain Nov 7, 2022, 9:30 PM

#

since redoing it is just running the script

fiery cosmos Nov 7, 2022, 9:31 PM

#

like everything in one line in a python script

#

then run that

flat hornet Nov 7, 2022, 9:31 PM

#

Guys in general, in big aplications do you develop a data structurs or use structurs of python, like lists, arrays?

haughty mountain Nov 7, 2022, 9:31 PM

#

fiery cosmos like everything in one line in a python script

not python script

opal oriole Nov 7, 2022, 9:31 PM

#

fiery cosmos like everything in one line in a python script

You can treat the script file as if you typed it into the terminal yourself.

#

It just does what you write in the terminal.

haughty mountain Nov 7, 2022, 9:32 PM

#

@fiery cosmos what platform are you on again?

fiery cosmos Nov 7, 2022, 9:32 PM

#

i mean like, everything in one line in a text editor?

haughty mountain Nov 7, 2022, 9:32 PM

#

one command per line

opal oriole Nov 7, 2022, 9:32 PM

#

One line per program execution / command.

fiery cosmos Nov 7, 2022, 9:32 PM

#

i'm on windows, i use powershell for unix/command line or w/e. my IDE is VScode

opal oriole Nov 7, 2022, 9:32 PM

#

On windows you make a batch file.

haughty mountain Nov 7, 2022, 9:33 PM

#

yeah, for this trivial usage they should behave the same

#

just write one command per line to a .bat file

#

run that

fiery cosmos Nov 7, 2022, 9:34 PM

#

so:
open notepad
write one command per line
save as .bat
run the .bat with.. command line?

haughty mountain Nov 7, 2022, 9:34 PM

#

python myfile.py --my --flags
python myfile.py --different --flags
...

opal oriole Nov 7, 2022, 9:34 PM

#

Command line or double click it, but it will close the terminal window immediately after finishing if you double click it to run.

#

You can add a "pause" as the last line.

#

Will wait for a key press to exit then.

#

(Then just double click the bat file to run)

fiery cosmos Nov 7, 2022, 9:38 PM

#

ok i think i've got it. just did a test with a single command

#

this is awesome

flat hornet Nov 7, 2022, 9:39 PM

#

Squiggle do you can explain for me about use of data struturs in system?

#

Or do you need understand how work only

#

because already are created in functions?

opal oriole Nov 7, 2022, 9:42 PM

#

flat hornet Squiggle do you can explain for me about use of data struturs in system?

Algorithms operate on data and that data needs to be stored somehow. A data structure is the specification of how that data is laid out.

haughty mountain Nov 7, 2022, 9:43 PM

#

fiery cosmos this is awesome

embrace laziness

fiery cosmos Nov 7, 2022, 9:43 PM

#

no this is so amazing that this works i've spent like 5 hrs before doing this manually

#

automatically naming output according to the inputs would have been cool too. next time

#

the other better thing about this is i can see every command all at once, and ensure i'm not rerunning things or overlooking things

opal oriole Nov 7, 2022, 9:45 PM

#

Naming output?

fiery cosmos Nov 7, 2022, 9:46 PM

#

right now i am manually passing an output name each time for a given input, eg, whatever text file name you write in

#

and actually, it'd probably error pretty bad if you named a non txt file

opal oriole Nov 7, 2022, 9:47 PM

#

You can have it write to stdout (the terminal, same as printing normally), and batch / bash lets you redirect such output to a file.

#

But i'm guessing they want you to write to a file.

flat hornet Nov 7, 2022, 9:47 PM

#

opal oriole Algorithms operate on data and that data needs to be stored somehow. A data stru...

but in real how is apply?

#

in a system?

opal oriole Nov 7, 2022, 9:48 PM

#

flat hornet but in real how is apply?

Systems operate on data and that data needs to be stored somehow. A data structure is the specification of how that data is laid out.

fiery cosmos Nov 7, 2022, 9:48 PM

#

opal oriole But i'm guessing they want you to write to a file.

correct

flat hornet Nov 7, 2022, 9:49 PM

#

opal oriole Systems operate on data and that data needs to be stored somehow. A data structu...

But data structurs work in data base?

#

or in code?

fiery cosmos Nov 7, 2022, 9:49 PM

#

alright let's try this bad boy

opal oriole Nov 7, 2022, 9:50 PM

#

flat hornet But data structurs work in data base?

class MyData:
  x = 10
  y = 20

#

(and many other ways)

fiery cosmos Nov 7, 2022, 9:51 PM

#

i think running that and having every input get run almost immediately is the most satisfying thing ive ever done in coding

#

watching out the outputs spring into existence with a single enter

#

i might be hooked y'all

flat hornet Nov 7, 2022, 9:52 PM

#

opal oriole ```py class MyData: x = 10 y = 20 ```

understand, but data structurs can connection with data base?

#

:

fiery cosmos Nov 7, 2022, 9:53 PM

#

hmm

#

my comparisons are a bit different, i guess that's ok

#

i'll update my graphs

opal oriole Nov 7, 2022, 9:53 PM

#

flat hornet understand, but data structurs can connection with data base?

A database is a system for managing data and the relationships within. It must have some layout for the data... (it must have some structure for the data)

fiery cosmos Nov 7, 2022, 9:56 PM

#

how will this batch file treat blanklines

opal oriole Nov 7, 2022, 9:57 PM

#

fiery cosmos how will this batch file treat blanklines

Like blank lines if you typed them into the terminal, so nothing.

fiery cosmos Nov 7, 2022, 9:57 PM

#

itll skip and continue though

opal oriole Nov 7, 2022, 9:57 PM

#

Imagine it auto types that file into the terminal for you.

#

Line by line.

#

It runs a "batch" of programs.

fiery cosmos Nov 7, 2022, 9:58 PM

#

i got you

bitter viper Nov 7, 2022, 11:17 PM

#

I have a file with records of how a user navigated through a website.
It is encoded as follows:
A;B;C;<;G;<;<;M
Where letters represent the current page and < represents the user clicking on the back button. Every action is separated by a semicolon. In the above example, the user started at A, navigated to B, then C, then back to B, then to G, then back to B, back to A, and from A to M

My objective is to track all the "movements" of the user in order to measure the popularity of each link. I decoded the path to a doubly-linked-list in order to navigate from the start point to the end point, counting each "jump" taken.

This requires a lot of resources since I have 100k paths to analyze and I was looking for an idea to optimize the process. Any suggestions?

agile sundial Nov 7, 2022, 11:22 PM

#

why a doubly linked list? and how do you measure popularity?

bitter viper Nov 7, 2022, 11:28 PM

#

Popularity is measured by frequency that a link is used.

Doubly linked because I decode the "path" and then traverse it to increase a variable storing the frequency each link was used.

I'm trying to find a way to decode and count at the same time, but can't put my finger on it

flat hornet Nov 7, 2022, 11:28 PM

#

opal oriole A database is a system for managing data and the relationships within. It must h...

Squiggle i can send message for you in private?

agile sundial Nov 7, 2022, 11:29 PM

#

so the < means the "parent" page is counted again?

bitter viper Nov 7, 2022, 11:30 PM

#

< means that the user went back to the parent page, and that the next link will be from (parent) to (other) page

agile sundial Nov 7, 2022, 11:30 PM

#

right, but how are you counting that in the frequency calculation

bitter viper Nov 7, 2022, 11:31 PM

#

< are not counted, only the next action will be

#

Therefore, A;B;<;D should give: one click on link to B from A, one click on link to D from A

agile sundial Nov 7, 2022, 11:32 PM

#

oh you need to track the links?

bitter viper Nov 7, 2022, 11:33 PM

#

Yes, the end objective is listing all the links out of page A and identifying the frequency that each one is used by the user

#

But I have thousands of "paths" from a user jumping around the website

agile sundial Nov 7, 2022, 11:33 PM

#

seems fairly trivial then. use a stack, when you see a letter, add to a Counter the link (the previous letter, the new letter). then pop if you see a <

bitter viper Nov 7, 2022, 11:34 PM

#

Mmh, makes a lot of sense.

#

No need for a full fledged linked list, a stack will do

agile sundial Nov 7, 2022, 11:34 PM

#

you could either split the string on ; or just iterate using indexes

#

well a stack could be implemented with a linked list. though python's list will be just fine (and probably better)

bitter viper Nov 7, 2022, 11:35 PM

#

Coming from C++ to Python has it's challenges

#

Thanks a lot -- will give it a try

agile sundial Nov 7, 2022, 11:36 PM

#

python's list is basically a std::vector

bitter viper Nov 7, 2022, 11:38 PM

#

Also for context, the project is based on this dataset https://snap.stanford.edu/data/wikispeedia.html
Where each page is an article with all outgoing links to other articles.
The goal is to analyze the popularity of outgoing links in articles based on their position, length of the word, etc.

undone sluice Nov 8, 2022, 2:08 AM

#

A(?=B) and A(?!B) both of them in regex is equivalent positive and negation in logic?

feral frigate Nov 8, 2022, 3:08 AM

#

How do I get good at solving Problem Solving questions?

unique topaz Nov 8, 2022, 3:16 AM

#

bitter viper Coming from C++ to Python has it's challenges

You will be fine. Wish I knew c++ 😔

grim bough Nov 8, 2022, 5:02 AM

#

https://stackoverflow.com/questions/74355848/equivalent-code-of-open-with-in-python-script

Stack Overflow

equivalent code of 'open with' in python script

import sys
sys. argv[1]

is the code equivalent of the above image. Please reply me

#

Is it true

#

?

fierce sluice Nov 8, 2022, 11:08 AM

#

I got a question
is there an equivalent to cpp's

set<pair<float, int>> my_set;
my_set.insert(pair<float, int>(1.2, 1));
my_set.insert(pair<float, int>(2.4, 2));
pair<float, int> min_number = *(my_set.begin());
my_set.erase(my_set.begin());

#

It gives the minimum in O(log(n))

#

So in other words, is there any way to get minimum in python O(log(n))?

austere sparrow Nov 8, 2022, 11:50 AM

#

fierce sluice So in other words, is there any way to get minimum in python O(log(n))?

If you already have a set?

#

Constructing the set is obviously O(n) already

#

There's a binary heap:

#

!d heapq

halcyon plankBOT Nov 8, 2022, 11:51 AM

#

heapq

Source code: Lib/heapq.py

This module provides an implementation of the heap queue algorithm, also known as the priority queue algorithm.

Heaps are binary trees for which every parent node has a value less than or equal to any of its children. This implementation uses arrays for which heap[k] <= heap[2*k+1] and heap[k] <= heap[2*k+2] for all k, counting elements from zero. For the sake of comparison, non-existing elements are considered to be infinite. The interesting property of a heap is that its smallest element is always the root, heap[0].

fierce sluice Nov 8, 2022, 1:14 PM

#

austere sparrow !d heapq

Thanks man

fiery cosmos Nov 8, 2022, 5:04 PM

#

is a print statement considered a return

haughty mountain Nov 8, 2022, 5:21 PM

#

fiery cosmos is a print statement considered a return

no pithink

fiery cosmos Nov 8, 2022, 5:22 PM

#

pithink

#

this batch file is saving my life rn

#

hmm

#

feel like i might be counting my chaining comparisons wrong

#

either that or it really is just wildly more efficient

#

yeah i added a comparison counter to my while loop

fiery cosmos Nov 8, 2022, 6:27 PM

#

if inserting n keys into a hashtable and each key takes time of O(n), it'd take n^2 time to insert them all?

haughty mountain Nov 8, 2022, 7:46 PM

#

fiery cosmos if inserting n keys into a hashtable and each key takes time of O(n), it'd take ...

yes

#

but insertion really shouldn't be O(n)

#

worst case yes, typical case no

fiery cosmos Nov 8, 2022, 7:48 PM

#

thanks i just wanted to ensure i had the logic correct

haughty mountain Nov 8, 2022, 7:48 PM

#

one thing that could be interesting is a scatter plot of the cost per inserted key, as you add keys

fiery cosmos Nov 8, 2022, 7:48 PM

#

i agree

#

i can say that it would look somewhere between exponential and linear for linear and quad probing, mostly linear in the case of chaining

#

chaining with a randomized stack is remarkably efficient, as measured by very low number of comparisons

haughty mountain Nov 8, 2022, 7:50 PM

#

what's the range for your random keys?

fiery cosmos Nov 8, 2022, 7:51 PM

#

for their input or my supplemental input

haughty mountain Nov 8, 2022, 7:51 PM

#

I guess both are interesting

fiery cosmos Nov 8, 2022, 7:51 PM

#

1s

haughty mountain Nov 8, 2022, 7:52 PM

#

what I'm curious about is really "do you expect any collisions?"

#

but knowing the range answers that

fiery cosmos Nov 8, 2022, 7:52 PM

#

theirs are 0-99,999

haughty mountain Nov 8, 2022, 7:53 PM

#

that seems fine

fiery cosmos Nov 8, 2022, 7:53 PM

#

mine are 0-90k

haughty mountain Nov 8, 2022, 7:54 PM

#

then you should get some random collisions

fiery cosmos Nov 8, 2022, 7:54 PM

#

haughty mountain but knowing the range answers that

i would have thought its more dependent upon the number of keys you try to insert

#

oh i get quite a few

#

let me share a graph

#

sry, this is comparisons

#

but the primary and secondary collisions end up adding up to this value

#

or somewhere similar

#

as expected, chaining is much more efficient

#

the amortization analysis of cost to insert keys could be interesting as a function of load factor

haughty mountain Nov 8, 2022, 7:56 PM

#

fiery cosmos i would have thought its more dependent upon the number of keys you try to inser...

it depends on the distribution of keys

fiery cosmos Nov 8, 2022, 7:56 PM

#

of course

#

if they are all the same, lots of collisions

haughty mountain Nov 8, 2022, 7:57 PM

#

say you insert numbers 1-120 in a table of size 120, with mod 120

#

no collisions

fiery cosmos Nov 8, 2022, 7:57 PM

#

should be near to zero

#

right

#

yeah i should really test input with many of the same key, and measure the comparisons required to enter all

#

but alas i am burnt out

haughty mountain Nov 8, 2022, 7:58 PM

#

I just wanted to make sure that you don't sample numbers between [0, tablesize) or something

fiery cosmos Nov 8, 2022, 7:58 PM

#

thanks for that

#

i'm a little bit brighter than that

#

slightly

#

😂

#

very pleased that you and squiggle got me going with the batch file

#

thats, a game changer

#

and as i have said before, i seriously hope i get to continue learning software dev because i really enjoy learning and troubleshooting

haughty mountain Nov 8, 2022, 8:00 PM

#

I tell you, laziness is great

#

automate the annoying things

fiery cosmos Nov 8, 2022, 8:01 PM

#

i see it as being more competent and automating things others simply don't know how to, but i appreciate the humbleness of describing it as lazy

haughty mountain Nov 8, 2022, 8:01 PM

#

even stuff like text editing can be automated with a powerful enough text editor 😛

vocal gorge Nov 8, 2022, 8:01 PM

#

oh, I thought you were going to say "github copilot" :p

haughty mountain Nov 8, 2022, 8:01 PM

#

fiery cosmos i see it as being more competent and automating things others simply don't know ...

hey, I put a lot of effort into being lazy!

vocal gorge Nov 8, 2022, 8:01 PM

#

~~so good at automation you automated yourself away~~

fiery cosmos Nov 8, 2022, 8:02 PM

#

vocal gorge ~~so good at automation you automated yourself away~~

lmao

haughty mountain Nov 8, 2022, 8:02 PM

#

(the secret is automating your work and not telling anyone, so people think you're working hard)

fiery cosmos Nov 8, 2022, 8:02 PM

#

my batch file open in a text editor was being really weird, instead of moving stuff when i tried to insert into the middle of a string line it started overwriting all the proceeding characters pithink

fiery cosmos Nov 8, 2022, 8:03 PM

#

haughty mountain (the secret is automating your work and not telling anyone, so people think you'...

that brilliant lol. i always wondered what level of that there is

haughty mountain Nov 8, 2022, 8:03 PM

#

insert mode

#

try pressing the insert key on your keyboard to toggle it

fiery cosmos Nov 8, 2022, 8:03 PM

#

oooooh, that's what that key does????

#

wow

#

TIL

#

must be a legacy thing

#

also, oddly enough the only way to open a batch file on windows (that i could find), was dragging it into an open text editor. if you double-click it'll just run itself and disappear

#

i should get on linux, i have always hated windows and having to be logged into certain softwares

haughty mountain Nov 8, 2022, 8:05 PM

#

my friend discovered that the insert key enters insert mode in vim, which I found bizarre

fiery cosmos Nov 8, 2022, 8:05 PM

#

something something surveillance

#

vim?

#

virtual machine?

haughty mountain Nov 8, 2022, 8:06 PM

#

fiery cosmos also, oddly enough the only way to open a batch file on windows (that i could fi...

you should be able to right click and edit

vocal gorge Nov 8, 2022, 8:06 PM

#

fiery cosmos also, oddly enough the only way to open a batch file on windows (that i could fi...

rightclick-Edit?

#

🥴

fiery cosmos Nov 8, 2022, 8:06 PM

#

lms

haughty mountain Nov 8, 2022, 8:06 PM

#

fiery cosmos vim?

vim is a text editor

fiery cosmos Nov 8, 2022, 8:06 PM

#

oh ok

haughty mountain Nov 8, 2022, 8:06 PM

#

quite old school text editor

#

but very powerful

#

(and very different from your usual text editors)

fiery cosmos Nov 8, 2022, 8:07 PM

#

oh i see why i didn't find it, in windows 11 they hide all that useful stuff from you, including copy

#

you have to go right click -> show more options -> edit

haughty mountain Nov 8, 2022, 8:07 PM

#

that's terrible

vocal gorge Nov 8, 2022, 8:07 PM

#

something something boiling frogs

fiery cosmos Nov 8, 2022, 8:07 PM

#

haughty mountain that's terrible

💯

#

truly awful, agree

vocal gorge Nov 8, 2022, 8:08 PM

#

in windows12 you'll have to enable these options in the settings first 😉

fiery cosmos Nov 8, 2022, 8:08 PM

#

lmao

#

confused with the jokes today

haughty mountain Nov 8, 2022, 8:08 PM

#

I'm living in a cozy terminal on linux since like a decade

fiery cosmos Nov 8, 2022, 8:09 PM

#

i've had every intention of going there, i've even partitioned my SSDs to make a linux enviro, never got around to it

#

how does it affect gaming

haughty mountain Nov 8, 2022, 8:09 PM

#

I don't use guis much unless it makes a lot of sense for them being guis, like web browser, image editing, and some other stuff pithink

haughty mountain Nov 8, 2022, 8:10 PM

#

fiery cosmos how does it affect gaming

depends on what you're playing

fiery cosmos Nov 8, 2022, 8:10 PM

#

have you heard of puter

haughty mountain Nov 8, 2022, 8:10 PM

#

a lot of stuff works fine, mutiplayer games that use anti-cheat are likely not going to work

#

even if the game itself would work

fiery cosmos Nov 8, 2022, 8:11 PM

#

oof that's a big ask. i guess one could always have one PC for gaming and one for everything else

#

https://puter.com/

Puter

Puter is a cloud operating system. Store, open, and edit your files from anywhere at any time in the cloud.

#

its an OS within a web browser

#

pretty cool

haughty mountain Nov 8, 2022, 8:12 PM

#

but most games I want to play kinda just work

#

because of big efforts from valve

fiery cosmos Nov 8, 2022, 8:13 PM

#

do you use steam

haughty mountain Nov 8, 2022, 8:13 PM

#

yeah

#

valve has proton which is a compatibility layer that allows running windows games on linux

#

(based on wine)

fiery cosmos Nov 8, 2022, 8:15 PM

#

never heard of proton or wine. sidebar my email carrier is protonmail

agile sundial Nov 8, 2022, 8:16 PM

#

just use WSL

fiery cosmos Nov 8, 2022, 8:16 PM

#

i really need to learn R but i prefer learning python and DS

#

what's wsl

vocal gorge Nov 8, 2022, 8:17 PM

#

why do you need to learn R?

agile sundial Nov 8, 2022, 8:18 PM

#

fiery cosmos what's wsl

basically a Linux vm

fiery cosmos Nov 8, 2022, 8:47 PM

#

vocal gorge why do you need to learn R?

im going into computational bio which is stats heavy

fiery cosmos Nov 8, 2022, 8:47 PM

#

agile sundial basically a Linux vm

yeah thats what i though thanks

fiery cosmos Nov 8, 2022, 9:38 PM

#

what is linear regression all about

haughty mountain Nov 8, 2022, 10:08 PM

#

fiery cosmos what is linear regression all about

fitting a line to data

fiery cosmos Nov 8, 2022, 10:10 PM

#

what is the purpose of it

#

what is multiple linear regression

gleaming pivot Nov 8, 2022, 10:18 PM

#

https://leetcode.com/discuss/interview-question/2786868/Python-BeginnerIntermediate-Guide-to-Functions-DS-and-Techniques

Level up your coding skills and quickly land a job. This is the best place to expand your knowledge and get prepared for your next interview.

fiery cosmos Nov 8, 2022, 10:21 PM

#

i don't think my explanation of insertion asymptotics is making sense

haughty mountain Nov 8, 2022, 10:30 PM

#

fiery cosmos what is the purpose of it

fitting a line to data

fiery cosmos Nov 8, 2022, 10:30 PM

#

lol bruh

agile sundial Nov 8, 2022, 10:31 PM

#

the number of people that buy ice cream if it costs 20 dollars is 50. the number of people that buy ice cream if it costs 10 dollars is 100. i wonder how many people will buy ice cream if it costs 5 dollars

fiery cosmos Nov 8, 2022, 10:33 PM

#

seems simple enough

azure osprey Nov 8, 2022, 10:45 PM

#

agile sundial the number of people that buy ice cream if it costs 20 dollars is 50. the number...

That is not a very accurate example. In reality, it should be more exponential than linear

agile sundial Nov 8, 2022, 10:46 PM

#

azure osprey That is not a very accurate example. In reality, it should be more exponential t...

let's say it's perfectly elastic :P

#

wait, why would it be exponential

azure osprey Nov 8, 2022, 10:46 PM

#

Well word spreads quick

#

Once things are cheap 😉

agile sundial Nov 8, 2022, 10:47 PM

#

that's not how it works

azure osprey Nov 8, 2022, 10:47 PM

#

Yea i was jk

#

But seriously irl it should be exponential

agile sundial Nov 8, 2022, 10:48 PM

#

idk about that

haughty mountain Nov 8, 2022, 11:00 PM

#

agile sundial the number of people that buy ice cream if it costs 20 dollars is 50. the number...

if you give it away for free you'll have infinite customers

#

and if you sell it 200, half of a person will buy it

#

idk if this model makes total sense 😛

agile sundial Nov 8, 2022, 11:02 PM

#

just floor it for the half a person case

#

and it does make sense for the free case if you change it from "how many people will buy it" to "how many people that are able and willing to buy it would buy it"

#

but anyways, it does work as an example

haughty mountain Nov 8, 2022, 11:06 PM

#

this feels related 😛

fiery cosmos Nov 8, 2022, 11:07 PM

#

"sublinear"

haughty mountain Nov 8, 2022, 11:07 PM

#

but yeah, basically you can use linear regressions to try to fit functions to data

#

(it's fairly basic linear algebra to do it)

fiery cosmos Nov 8, 2022, 11:09 PM

#

just for modelling? or like, what's the primary purpose. is it the same as linear regression analysis? what is multiple linear regression? why is there an entire branch of algebra dedicated to lines (actually, your previous post gives me some idea)

haughty mountain Nov 8, 2022, 11:10 PM

#

fiery cosmos just for modelling? or like, what's the primary purpose. is it the same as linea...

I have data, it seems to have a pattern, let me try to fit a function like the pattern, how good of a fit is it?

haughty mountain Nov 8, 2022, 11:11 PM

#

fiery cosmos just for modelling? or like, what's the primary purpose. is it the same as linea...

it's not only lines, you can fit other stuff with linear regression

fiery cosmos Nov 8, 2022, 11:12 PM

#

haughty mountain (it's fairly basic linear algebra to do it)

i was referring to linear algebra

haughty mountain Nov 8, 2022, 11:13 PM

#

haughty mountain it's not only lines, you can fit other stuff with linear regression

e.g. I could try fitting functions on the form y = c1*x + c2*exp(x) + c3*whateveryouwant(x) + c4 to some data

#

the linear algebra part is how the constants are picked

#

linear algebra is really about linear combinations of stuff, not just about lines

fiery cosmos Nov 8, 2022, 11:15 PM

#

are those not the same things

agile sundial Nov 8, 2022, 11:19 PM

#

no, see his example, he has 4 things that might vary, which gives a 4 dimensional thing, not a line

fiery cosmos Nov 8, 2022, 11:20 PM

#

so a line must then be just a single equation

#

of multiple terms

#

which can each vary?

agile sundial Nov 8, 2022, 11:21 PM

#

his example is a single equation. a line is an equation with 1 varying thing, essentially

fiery cosmos Nov 8, 2022, 11:21 PM

#

in what way is that not the same

agile sundial Nov 8, 2022, 11:21 PM

#

well a line is something like ax = b, right. a plane could be something like ax + by = c a 3 dimensional surface could be something like ax + by + cz = d

lean lake Nov 8, 2022, 11:28 PM

#

hello all! im learning DS and im kinda stuck.

so i made a random walk function that uses an adjacency list (from a dictionary) .. where would i start if i had to modify my code so that it can use a weighted adjacency matrix instead?

def random_walk(graph, nodeid, steps):
    da_walk = [nodeid]
    while len(da_walk) < steps:
        nodeid = random.choice(list(graph[nodeid]))
        da_walk.append(nodeid)
        turns = steps - 1
        random_walk(graph, nodeid, turns)
    return da_walk

glossy breach Nov 9, 2022, 11:46 AM

#

Basically the same thing but use a list of tuples (id, weight) in your adjacency list instead of just id

fiery cosmos Nov 9, 2022, 3:11 PM

#

which books are good to learn ALGO and DS using python

haughty mountain Nov 9, 2022, 5:41 PM

#

none of them are super easy

fiery cosmos Nov 9, 2022, 5:41 PM

#

which several are the least difficult

haughty mountain Nov 9, 2022, 5:41 PM

#

multithreaded algos is kind of a no-go in python

#

polynomials and fft is a fun topic

fiery cosmos Nov 9, 2022, 5:42 PM

#

ok, that's super helpful to know bc i was leaning that way

fiery cosmos Nov 9, 2022, 5:42 PM

#

haughty mountain polynomials and fft is a fun topic

fun for the mathematically competent

haughty mountain Nov 9, 2022, 5:43 PM

#

most of these are pretty mathy

#

it's fun because the naive way of multiplying polynomials is O(n²) where n is the degree

#

with fft you can do it in O(n log n)

#

string matching might not be hard, but it very much depends on what's covered

#

there is a ton of stuff in that bucket

fiery cosmos Nov 9, 2022, 5:45 PM

#

i mean this'll all be straight out of CLRS, so whatever they cover in there

haughty mountain Nov 9, 2022, 5:45 PM

#

yes, and idk what that is without having to look it up

fiery cosmos Nov 9, 2022, 5:45 PM

#

lms

haughty mountain Nov 9, 2022, 5:46 PM

#

computational geometry is so very fiddly

#

linear programming is a pretty huge topic with a lot of theory around it

#

idk what they cover in number theoretic algorithms

fiery cosmos Nov 9, 2022, 5:47 PM

#

i've x'd that out bc there is a ton of subject matter

#

like more than double the concepts of other chapters

#

if you're curious i can put it here

agile sundial Nov 9, 2022, 5:48 PM

#

fft for polynomials sounds really cool

fiery cosmos Nov 9, 2022, 5:48 PM

#

that's definitely on the list

#

need to pick several

#

sounds like polys and fft, string matching, and one more

haughty mountain Nov 9, 2022, 5:49 PM

#

the number theory topics looks fun though

agile sundial Nov 9, 2022, 5:49 PM

#

yeah those look useful

#

I'm learning those right now in school lol

fiery cosmos Nov 9, 2022, 5:50 PM

#

those stars mean grad school topics tho

#

meaning more difficult

agile sundial Nov 9, 2022, 5:50 PM

#

no it just means hard

fiery cosmos Nov 9, 2022, 5:50 PM

#

right

agile sundial Nov 9, 2022, 5:50 PM

#

any section will have those, though

fiery cosmos Nov 9, 2022, 5:51 PM

#

chpt 30 has only 3 subjects and none are starred

haughty mountain Nov 9, 2022, 5:52 PM

#

fwiw chapter 30 will involve some complex math

fiery cosmos Nov 9, 2022, 5:52 PM

#

i don't think anyone in my group has a math background

haughty mountain Nov 9, 2022, 5:53 PM

#

(as in complex numbers, not necessarily so complicated)

fiery cosmos Nov 9, 2022, 5:53 PM

#

we're a ragtag bunch of like virus people and fresh from undergrad ppl

agile sundial Nov 9, 2022, 5:54 PM

#

and fft, which is somewhat complicated

fiery cosmos Nov 9, 2022, 5:54 PM

#

i don't think the majority of math is necessarily that complex, i just think its a matter of not knowing it

#

is an issue

#

bc then you have to pause everything and try to go learn it

#

i mean obviously there is some very difficult math yes

haughty mountain Nov 9, 2022, 6:00 PM

#

agile sundial and fft, which is somewhat complicated

cooley-tukey isn't too bad

#

it's just a bunch of even-odd splits

fiery cosmos Nov 9, 2022, 6:02 PM

#

are B-trees still used? i think someone said for databases they are often used?

#

there are no spinning discs in my PC 🤷‍♂️

agile sundial Nov 9, 2022, 6:02 PM

#

ram is still much faster than SSDs, so they're still useful

fiery cosmos Nov 9, 2022, 6:04 PM

#

the book starts with showing a spinning HDD as soon as B-trees come up

haughty mountain Nov 9, 2022, 6:04 PM

#

aren't B-trees better BBSTs anyway?

#

in terms of memory usage and cache locality

agile sundial Nov 9, 2022, 6:05 PM

#

that's what I thought

agile sundial Nov 9, 2022, 6:05 PM

#

fiery cosmos the book starts with showing a spinning HDD as soon as B-trees come up

because it's old, but it's the same idea

fiery cosmos Nov 9, 2022, 6:05 PM

#

one node can have a thousand children???

#

dog

haughty mountain Nov 9, 2022, 6:05 PM

#

so if you want something like an always sorted set, B trees are great

#

#

slightly better 😛

#

you lose some guarantees of BBSTs, but nothing overly useful

#

like, if I have a pointer to an element in the set and I delete some element, is that pointer still valid?

fiery cosmos Nov 9, 2022, 6:09 PM

#

is there a formal definition of a pointer? for me its sort of like a murky concept

haughty mountain Nov 9, 2022, 6:09 PM

#

fiery cosmos is there a formal definition of a pointer? for me its sort of like a murky conce...

basically the address to somewhere in memory

fiery cosmos Nov 9, 2022, 6:09 PM

#

like when we just made bucket.pointer = some other bucket

agile sundial Nov 9, 2022, 6:09 PM

#

it's similar to an int with a value that's a memory address

haughty mountain Nov 9, 2022, 6:10 PM

#

fiery cosmos like when we just made bucket.pointer = some other bucket

those aren't really pointers in the formal sense

#

but indices

fiery cosmos Nov 9, 2022, 6:11 PM

#

yes, it was just pointing at an index in the table

#

ill do some reading

#

rn i need to figure out this B-tree problem

#

how do memory addresses on the RAM work? is there like a mapping to individual bytes / bits ?

#

is that done by the RAM manufacturer or the OS

haughty mountain Nov 9, 2022, 6:23 PM

#

bytes, OS

fiery cosmos Nov 9, 2022, 6:44 PM

#

i'm not understanding the third property of B-trees:
3. the keys x.key_i separate the ranges of keys stored in each subtree: if k_i is any key stored in the subtree with root x.c_i, then
k_1 <= x.key_1 <= k_2 <= x.key_2 <= ... <= x.key_x.n <= k_x.n+1

#

#

and a byte is 8 bits (the part of the semiconductor that can be either 0 or 1)

#

trivia (without looking): what is the name for a string of four bits

fiery cosmos Nov 9, 2022, 7:23 PM

#

inserting into B-trees is rather involved

#

splitting nodes and adding the median key to its parent

median trout Nov 9, 2022, 8:27 PM

#

Hey guy's a beginning programmer here with a question; I plugged the following formula into a variable and I get the following TypeErrors:

#

But if I split the problem up into seperate expressions it will run fine. can anyone tell me why?

gusty geode Nov 9, 2022, 8:47 PM

#

median trout But if I split the problem up into seperate expressions it will run fine. can an...

do int()

#

num() actually

median trout Nov 9, 2022, 8:49 PM

#

do int() on the whole mathematical expression? there is no built in function called num()

gusty geode Nov 9, 2022, 8:50 PM

#

oh shoot I was thinking about a module that I'm used to using

fiery cosmos Nov 9, 2022, 8:52 PM

#

i don't understand the predecessor subgraph of BFS

#

what is it

#

it notated as G_pi

gusty geode Nov 9, 2022, 8:53 PM

#

median trout But if I split the problem up into seperate expressions it will run fine. can an...

pop = (1000*(1.02*0.001)**0.001)+50+0.0001 should work

median trout Nov 9, 2022, 8:54 PM

#

that's what I thought but obviously I am wrong.

gusty geode Nov 9, 2022, 8:54 PM

#

or are you not trying to multiply it by 1000?

median trout Nov 9, 2022, 8:54 PM

#

you can see I changed them all to floats it made no difference

gusty geode Nov 9, 2022, 8:56 PM

#

nope I just tested it and it worked

#

you forgot to add the * between (1000*(...

median trout Nov 9, 2022, 9:00 PM

#

oh, ok duh. I feel stupid now. Thank you

haughty mountain Nov 9, 2022, 9:13 PM

#

fiery cosmos trivia (without looking): what is the name for a string of four bits

nibble

fiery cosmos Nov 9, 2022, 9:13 PM

#

yooo good job

#

did you really know that off the top of your head??

haughty mountain Nov 9, 2022, 9:14 PM

#

technically a byte could be different from 8 bits, but not on modern and non-exotic platforma

#

if you want to be super pedantic 8 bits is an octet

fiery cosmos Nov 9, 2022, 9:15 PM

#

8 bits = octet = 1 byte

haughty mountain Nov 9, 2022, 9:15 PM

#

fiery cosmos did you really know that off the top of your head??

isn't it common knowledge? 😛

fiery cosmos Nov 9, 2022, 9:15 PM

#

bruh

haughty mountain Nov 9, 2022, 9:16 PM

#

The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer

#

so there have been different byte sizes historically

#

I think 7 was kinda common for a bit

fiery cosmos Nov 9, 2022, 9:17 PM

#

so there is an interesting implication of self vs. non-self in many things, one of them being the immune system, i wonder if it is the same in computers

#

and how the concept of sameness manifests

#

eg, how does a computer know an if check is same or non-same. i guess everything just has its own machine-code representation

#

but like, how does it know

if pi == pi```

#

or similar

#

not important

#

#

good old predecessor subgraphs, you gotta love em

opal oriole Nov 9, 2022, 9:21 PM

#

fiery cosmos did you really know that off the top of your head??

It shows up commonly, specifically when doing bit manipulation and hexadecimal (1 digit).

haughty mountain Nov 9, 2022, 9:25 PM

#

yeah, 1 hex digit is a nibble

haughty mountain Nov 9, 2022, 9:25 PM

#

fiery cosmos but like, how does it know ```py if pi == pi```

compare bits

haughty mountain Nov 9, 2022, 9:28 PM

#

fiery cosmos

it took me a bit to realize what they were trying to say

fiery cosmos Nov 9, 2022, 9:28 PM

#

so it'd be like
is 10110110 = 10110110?

fiery cosmos Nov 9, 2022, 9:29 PM

#

fiery cosmos

i can read it from this into english in my head but haven't yet made sense of it

haughty mountain Nov 9, 2022, 9:31 PM

#

!e

import math, struct
print(struct.pack('d', math.pi).hex())

halcyon plankBOT Nov 9, 2022, 9:31 PM

#

@haughty mountain :white_check_mark: Your 3.11 eval job has completed with return code 0.

182d4454fb210940

haughty mountain Nov 9, 2022, 9:32 PM

#

that's pi

#

8 bytes of data

fiery cosmos Nov 9, 2022, 9:33 PM

#

looks like a lot more than 8, if each letter is 1 byte = 8 bits

haughty mountain Nov 9, 2022, 9:33 PM

#

haughty mountain yeah, 1 hex digit is a nibble

this

fiery cosmos Nov 9, 2022, 9:34 PM

#

i thought 1 bit was a single either 0 or 1

haughty mountain Nov 9, 2022, 9:34 PM

#

yes

#

!e

import struct, math
print(struct.pack('d', math.pi).hex('|', 1))

halcyon plankBOT Nov 9, 2022, 9:35 PM

#

@haughty mountain :white_check_mark: Your 3.11 eval job has completed with return code 0.

18|2d|44|54|fb|21|09|40

haughty mountain Nov 9, 2022, 9:35 PM

#

easier to count now

stray fractal Nov 9, 2022, 9:35 PM

#

haughty mountain !e ```py import struct, math print(struct.pack('d', math.pi).hex('|', 1)) ```

TIL bytes.hex()

haughty mountain Nov 9, 2022, 9:36 PM

#

it's kinda neat

haughty mountain Nov 9, 2022, 9:36 PM

#

fiery cosmos i thought 1 bit was a single either 0 or 1

4 bits as an int can take values 0b0000 (0) to 0b1111 (15)

#

so it's a base 16 digit

#

2 of those gets us a byte

#

I could convert that hex into an int and get the parts of the double pithink

fiery cosmos Nov 9, 2022, 9:39 PM

#

i'll need to look up some sort of graphic. i'm not seeing where you got from 0's and 1's to

fiery cosmos Nov 9, 2022, 9:40 PM

#

halcyon plank <@133944101929222144> :white_check_mark: Your 3.11 eval job has completed with r...

this

fiery cosmos Nov 9, 2022, 9:40 PM

#

haughty mountain 4 bits as an int can take values 0b0000 (0) to 0b1111 (15)

oh its here

#

definition of predecessor subgraph is on pg. 600, pretty much the same as shown above

#

i'm noting that V_pi has a U {s} and E_pi has a - {s}

haughty mountain Nov 9, 2022, 9:50 PM

#

haughty mountain I could convert that hex into an int and get the parts of the double <:pithink:6...

!e magic

import struct, math

x = int(struct.pack('>d', math.pi).hex(), 16)
sign = x >> 63  # 1 bit at 63
exponent = x >> (63 - 11) & ((1<<11) - 1)  # 11 bits starting at 62
mantissa = x & ((1<<52) - 1)  # lowest 52 bits

print('+-'[sign], (2**52 + mantissa) * 2**(exponent - 1024 - 51))

halcyon plankBOT Nov 9, 2022, 9:50 PM

#

@haughty mountain :white_check_mark: Your 3.11 eval job has completed with return code 0.

+ 3.141592653589793

fiery cosmos Nov 9, 2022, 9:51 PM

#

Gπ = (Vπ, Eπ) where: Vπ = {v ∈ V : v.π =/= NIL} U {s} and Eπ = {(v.π, v) : v ∈ Vπ - {s}}

haughty mountain Nov 9, 2022, 9:53 PM

#

Vπ is all the vertices with a predecessor + the source (root)

#

Eπ are the edges that goes from vertices v in Vπ to their predecessor π[v]

#

err, ignoring the source in the second one

fiery cosmos Nov 9, 2022, 9:55 PM

#

"the predecessor subgraph G is a graph comprised of sets V predecessor and E predecessor where the set of predecessor nodes V is equal to the set of vertex v in the set of vertices V such that v's predecessor is not equal to None, union source node s, and. the set of predecessor edges are equal to (a vertex v's predecessor, v) edge such that vertex v is in the set of predecessor vertices V minus the set containing the source vertex s."

haughty mountain Nov 9, 2022, 9:56 PM

#

I read π as "parent" in my head here 😛

haughty mountain Nov 9, 2022, 9:57 PM

#

haughty mountain !e magic ```py import struct, math x = int(struct.pack('>d', math.pi).hex(), 16...

no love for my magic trick 😦

fiery cosmos Nov 9, 2022, 9:57 PM

#

they use ancestor and descendent in this bit

#

i was going to say, there is someone else more mathematically inclined which will have a proper appreciation for the mathematical gymnastics you are doing up there, as for myself, it was one big whoosh

haughty mountain Nov 9, 2022, 9:58 PM

#

fiery cosmos i was going to say, there is someone else more mathematically inclined which wil...

so, the first line is me getting the 8 bytes representing the python float as an int

#

then I extract all the parts of the floating point number (sign, exponent, mantissa)

#

and rebuild the number

fiery cosmos Nov 9, 2022, 10:00 PM

#

what are these symbols: >> <<, what is mantissa???

haughty mountain Nov 9, 2022, 10:00 PM

#

haughty mountain !e magic ```py import struct, math x = int(struct.pack('>d', math.pi).hex(), 16...

@brisk saddle do you like my magic trick?

brisk saddle Nov 9, 2022, 10:00 PM

#

aawhat the FUCK

haughty mountain Nov 9, 2022, 10:01 PM

#

fiery cosmos what are these symbols: `>>` `<<`, what is mantissa???

bit shifts

fiery cosmos Nov 9, 2022, 10:01 PM

#

i'm over here trying to understand graphs and dude is reconstructing pi using bits for fun

brisk saddle Nov 9, 2022, 10:02 PM

#

haughty mountain <@191434789444780033> do you like my magic trick?

can i humbly request

#

that you stop coding forever

haughty mountain Nov 9, 2022, 10:02 PM

#

floating point numbers are basically scientific notation but in binary

stray fractal Nov 9, 2022, 10:02 PM

#

haughty mountain !e magic ```py import struct, math x = int(struct.pack('>d', math.pi).hex(), 16...

i could say << should not be used in place of * but it gets optimized anyway and i don't like the look of 2**x (which gets optimized anyway as well)

brisk saddle Nov 9, 2022, 10:02 PM

#

your a floating point

haughty mountain Nov 9, 2022, 10:03 PM

#

1.(mantissa bits) * 2**(exponent bits - 1024)

#

and then the sign bit

fiery cosmos Nov 9, 2022, 10:03 PM

#

brisk saddle that you stop coding forever

lmao

haughty mountain Nov 9, 2022, 10:04 PM

#

stray fractal i could say `<<` should not be used in place of `*` but it gets optimized anyway...

I used the << and >> when I was thinking in bit operations

#

shifting and masking

fiery cosmos Nov 9, 2022, 10:04 PM

#

thinking in bit operations

nope

haughty mountain Nov 9, 2022, 10:04 PM

#

brisk saddle that you stop coding forever

you've never done this? 😛

brisk saddle Nov 9, 2022, 10:05 PM

#

do i look like someone who would dothis

haughty mountain Nov 9, 2022, 10:05 PM

#

kinda

#

you've done weirder things

#

I know more magic tricks

fiery cosmos Nov 9, 2022, 10:06 PM

#

is there a magic trick for making me understand all the crap in all these chapters all at once

#

like the matrix for CLRS

haughty mountain Nov 9, 2022, 10:08 PM

#

!e rounding

print(123.45 + 2**52 - 2**52)
print(123.54 + 2**52 - 2**52)

halcyon plankBOT Nov 9, 2022, 10:08 PM

#

@haughty mountain :white_check_mark: Your 3.11 eval job has completed with return code 0.

001 | 123.0
002 | 124.0

haughty mountain Nov 9, 2022, 10:09 PM

#

@brisk saddle I probably showed this one before

brisk saddle Nov 9, 2022, 10:09 PM

#

haughty mountain you've done weirder things

🥴

brisk saddle Nov 9, 2022, 10:09 PM

#

haughty mountain !e rounding ```py print(123.45 + 2**52 - 2**52) print(123.54 + 2**52 - 2**52) ``...

ugh, floating points are cursed

haughty mountain Nov 9, 2022, 10:10 PM

#

if you ignore nan inf and subnormals they are very well behaved

#

the + - trick is kinda dumb

fiery cosmos Nov 9, 2022, 10:11 PM

#

!e
x = 5318008
x.reverse()
print(x)

halcyon plankBOT Nov 9, 2022, 10:11 PM

#

@fiery cosmos :x: Your 3.11 eval job has completed with return code 1.

001 | Traceback (most recent call last):
002 |   File "<string>", line 2, in <module>
003 | AttributeError: 'int' object has no attribute 'reverse'

fiery cosmos Nov 9, 2022, 10:11 PM

#

bruh

haughty mountain Nov 9, 2022, 10:13 PM

#

haughty mountain the + - trick is kinda dumb

basically say I asked you to keep track of exactly 4 significant digits of this number, rounding if needed

start with say 123.4

#

I add 1000

#

1123.4

#

you round to keep 4 digits: 1123

haughty mountain Nov 9, 2022, 10:13 PM

#

haughty mountain you round to keep 4 digits: 1123

I subtract 1000: 123

#

!e this?

x = str(5318008)
x = x[::-1]
print(x)

halcyon plankBOT Nov 9, 2022, 10:15 PM

#

@haughty mountain :white_check_mark: Your 3.11 eval job has completed with return code 0.

haughty mountain Nov 9, 2022, 10:16 PM

#

and very mature 😛

fiery cosmos Nov 9, 2022, 10:17 PM

#

lol i knew there was a reverse slicing method to go through it. and yeah, that's the only numbers related thing from my childhood i could dream up

lean lake Nov 9, 2022, 11:04 PM

#

#help-cookie i need some pointers to get me unstuck in my DS class. im kind of struggling atm. thanks

lean lake Nov 10, 2022, 1:03 AM

#

@haughty mountain took me some time, but it's working now! thanks for pushing me in the right direction!

G2 = np.array([
    [0,    0.5,  0,    0.5],
    [0.5,  0,    0,    0.5],
    [0.25, 0.25, 0.25, 0.25],
    [0.5,  0.5,  0,    0],
])

GG2 = nx.from_numpy_matrix(G2, create_using=nx.DiGraph)


def random_walk2(graph, nodeid, steps, da_walk=None):
    if da_walk is None:
        da_walk = []
    da_walk.append(nodeid)

    if steps == 1:
        return da_walk

    nodeid = random.choices(list(GG2[nodeid]), weights=[k["weight"] for k in list(GG2[nodeid].values())])[0]

    return random_walk2(graph, nodeid, steps-1, da_walk)


print(random_walk2(GG2, 0, 4))

fiery cosmos Nov 10, 2022, 4:38 AM

#

my friend made similar looking diagrams when making a regex parser

static veldt Nov 10, 2022, 9:13 AM

#

'hello'

#

`helo1

#

    base=input('what is the base of the triangle:')
    def basecalculator(base):
        try:
            newbase=int(base)
            return newbase
        except:
            inp=input('enter an integer')
            basecalculator(inp)
    height=input('what is the height of the triangle:')
    def heightcalculator(height):
        try:
            newheight=int(height)
            return newheight
        except:
            inp=input('enter an integer')
            heightcalculator(inp)
    beforearea=basecalculator(base)*heightcalculator(height)
    finalarea=beforearea/2
    return finalarea
print('your area is',trianglecalculator())```

static veldt Nov 10, 2022, 9:15 AM

#

static veldt ```def trianglecalculator(): base=input('what is the base of the triangle:')...

hey guys im new to programming and ive run into this problem where my python program cant handle an error

#

and i dont know what else to do

#

is anyone free to help

hot latch Nov 10, 2022, 3:07 PM

#

Hey I've been trying t do this leetcode problem for a while and am still having some issues

#

#

do you guys have any ideas on hwo to do it?

#

so we need to choose m-1 rows that maximizes the minimum of the maximum of each column

#

I guess the brute force is simple but I don't nkow how to optimize the problem

agile geyser Nov 10, 2022, 3:47 PM

#

what would be the time complexity of

#

would it look something like O(log(nCr)) ?

signal ocean Nov 10, 2022, 4:01 PM

#

#Create a code generator. This can that take text as input, replaces 
#each letter with another letter, and outputs the “encoded” message.

string = input("What message would you like to be encoded? ")
key = input("Key: ")
#/.string = "abcdefg" # Used for testing
#/.key = 2
enc = ""

for i in range(len(string)):
    enc += chr(ord(string[i])+key)

print("The encrypted message is: ", enc)

Anyone able to figure out why my code doesn't work? At the moment I know it has something to do with how I'm shifting the characters. This line:
enc += chr(ord(string[i])+key)

plush wraith Nov 10, 2022, 4:08 PM

#

Dynamic programming algorithms improve time efficiency by efficient sorting algorithms.
is it true?

fiery cosmos Nov 10, 2022, 4:22 PM

#

no

#

dynamic programming algos improve efficiency by maintaining a table and looking up answers rather than re-computing subproblems

wise verge Nov 10, 2022, 4:52 PM

#

signal ocean ``` #Create a code generator. This can that take text as input, replaces #each ...

Are you getting an error message?

signal ocean Nov 10, 2022, 4:53 PM

#

Yes

#

The error tells me there's a problem with me using the utf-8

#

Nvm, I found something similar to the way I want to do it and I'll be looking at it before I ask more questions

haughty mountain Nov 10, 2022, 7:04 PM

#

hot latch so we need to choose m-1 rows that maximizes the minimum of the maximum of each ...

another view: I get to remove one row, which one should I remove?

#

am I dumb or isn't that solution super greedy?

#

you want to maximize the minimum

#

to increase this you need to remove some existing minimum

#

so you can just remove some row that contains the minimum

#

why is picking any such row ok? because if there are many rows with a minimum you're screwed anyway

#

so remove one row containing a minimum, compute the result, done

#

yeah, I think that should work

fiery cosmos Nov 10, 2022, 7:57 PM

#

i've been drawing pictures on trees for hrs, i feel like there is something wrong w a problem statement in the book

haughty mountain Nov 10, 2022, 7:59 PM

#

give the statement then

fiery cosmos Nov 10, 2022, 7:59 PM

#

so i made a B-tree

#

and i've been drawing what each of the sets looks like

#

not seeing how a path can split the S' set given that by definition is it every key smaller than key k

#

they're saying the S' set is the set of trees with keys smaller than k

#

so how could the path split that further when it is sort of already upper bounding it

#

let me give an example B-tree

#

i drew another tree with more keys, since nodes with 3 keys will have 4 pointers

#

and give the range that is specified by each key of a tree

haughty mountain Nov 10, 2022, 8:05 PM

#

where is the problem in the book?

hybrid epoch Nov 10, 2022, 8:09 PM

#

What book?

#

If you don't mind sharing

fiery cosmos Nov 10, 2022, 8:10 PM

#

the only conclusion i could draw is that you follow different pointers leaving the node on the path to the children while each key k is less than the search k (terrible way of explaining it)

fiery cosmos Nov 10, 2022, 8:10 PM

#

hybrid epoch What book?

intro to algorithms 3rd edition

#

do b-trees require latches?

fiery cosmos Nov 10, 2022, 8:48 PM

#

also stuck on another one if n e 1 is bored

wraith solar Nov 10, 2022, 10:44 PM

#

r

fiery cosmos Nov 11, 2022, 11:09 AM

#

I want to learn DSA in one month

#

is it possible?

dreamy valley Nov 11, 2022, 11:13 AM

#

Enough to pass an interview or final exam? Probably

vocal gorge Nov 11, 2022, 11:13 AM

#

well, in universities DSA is usually a semester or two (source: googled syllabus dsa course), so a month seems doable if you can go through it at several times the rate.

eager scroll Nov 11, 2022, 12:21 PM

#

hi

#

i have a list removable
removable = [3,1,0]
I have to remove those indexes characters from a string to create a new string
upto certain range
how to do it

       c=removable[i]
       temp=temp[:c]+temp[c+1:]

summer fossil Nov 11, 2022, 1:01 PM

#

Hii, You yeah You
Can u fix my code

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right

def height(root):
    if root==None:
        return 0
    return max((1+height(root.left)), (1+height(root.right)))

class Solution:
    
    def zigzagLevelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
        h = height(root)
        lis = []

        def fun(root, level, q):
            if root == None:
                return 0
            
            if level == 1:
                lis.append(root.val)

            elif level != 1 and q == True:
                fun(root.left, level-1, True)
                fun(root.right, level-1, True)

            elif level != 1 and q == False:
                fun(root.right, level-1, False)
                fun(root.left, level-1, False)

        for i in range(1, h+1):
            if i%2==0:
                fun(root, i, False)
            else:
                fun(root, i, True)

        return lis

Output:= [[3],[20,9],[15,7]]
myoutput = TypeError: [3, 20, 9, 15, 7] is not valid value for the expected return type list<list<integer>>

Thanks!

#

question:=https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/description/```

dreamy valley Nov 11, 2022, 1:10 PM

#

summer fossil Hii, You yeah You Can u fix my code ```py # Definition for a binary tree node. #...

well, it looks like you want each level of the tree to be in its own list
so you can't just add them all to the same list, you need to make a new list at each height

summer fossil Nov 11, 2022, 1:11 PM

#

dreamy valley well, it looks like you want each level of the tree to be in its own list so you...

like height list = [] * height

haughty mountain Nov 11, 2022, 3:28 PM

#

[] * height is a fun way to spell []

hybrid epoch Nov 11, 2022, 3:32 PM

#

summer fossil Hii, You yeah You Can u fix my code ```py # Definition for a binary tree node. #...

It looks like you're correctly doing the zigzag level traversal at each iteration of your for loop. Why not create a new list, say L, append lis to that, then 'reset' lis with each iteration ?

pearl ridge Nov 11, 2022, 3:57 PM

#

if a method uses a method that is O(n) then is that method also of the same time complexity?

vocal gorge Nov 11, 2022, 3:58 PM

#

well, of at least that time complexity

#

if it calls it O(n) times, that's O(n^2) complexity already

fiery cosmos Nov 11, 2022, 4:50 PM

#

oof i'm finally at NP-completeness, may god have mercy on my soul

fiery cosmos Nov 11, 2022, 6:18 PM

#

so all this mess about encoding problem instances as languages / in binary certificates is just to formalize the P and NP classes yes?

#

does one ever actually have to pass binary certificates as arguments to their algo or this this just how to build a formal problem instance into a language?

#

from the book:
a verification algorithm a two-argument algorithm A where one input is an ordinary string x and the other is a binary string y called a certificate. a two argument algorithm A verifies an input string x if there exists a certificate y such that A(x, y) = 1

#

the language verified by a verification algorithm A is
L = {x ∈ {0, 1}* : there exists y ∈ {0, 1}* such that A(x, y) = 1}

fiery cosmos Nov 11, 2022, 6:47 PM

#

this is really cool:
https://en.wikipedia.org/wiki/Deterministic_algorithm#Disadvantages_of_determinism

#

you use a hardware random number generator to get a randomized input seed to pre-program https://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator

Cryptographically secure pseudorandom number generator

A cryptographically secure pseudorandom number generator (CSPRNG) or cryptographic pseudorandom number generator (CPRNG) is a pseudorandom number generator (PRNG) with properties that make it suitable for use in cryptography. It is also loosely known as a cryptographic random number generator (CRNG) (see Random number generation § "True" vs. pse...

timber fox Nov 11, 2022, 6:58 PM

#

Can anyone here help me how to start with data structures in python??

#

Like any books? To learn DSA in python

fiery cosmos Nov 11, 2022, 6:59 PM

#

the main book of the field is language-agnostic. it contains pseudocode

timber fox Nov 11, 2022, 7:02 PM

#

Sorry could you please simplify it?? I didn't get you

fiery cosmos Nov 11, 2022, 7:04 PM

#

the main book that is used to teach algorithms does not use a specific language, and there is good reason for that

timber fox Nov 11, 2022, 7:05 PM

#

Oh ok

fiery cosmos Nov 11, 2022, 7:05 PM

#

if you want online courses that are python-specific, use EdX

#

maybe

#

although the python courses i took on there were about dictionaries and the like, nothing about real DS or algos

#

https://www.amazon.com/Introduction-Algorithms-3rd-MIT-Press/dp/0262033844

Introduction to Algorithms, 3rd Edition (The MIT Press)

#

this is the primary book for DS/algo

timber fox Nov 11, 2022, 7:06 PM

#

Thanka a lot sir

fiery cosmos Nov 11, 2022, 7:06 PM

#

also pins in this channel

#

is the MIT opencourseware version of that book

fiery cosmos Nov 11, 2022, 8:21 PM

#

oof

#

this 3CNF stuff is pretty brutal

haughty mountain Nov 11, 2022, 9:43 PM

#

fiery cosmos does one ever actually have to pass binary certificates as arguments to their al...

these are more for the sake of formality

#

the study of NP hard problems boils down to being able to show things like problem A is easier than problem B

#

this is true if I can translate a problem of type A into type B

#

because if I can solve B I can by extension solve A

#

that's the basic idea, but there are loads of details to make it formal

#

viable as in will eventually get the right answer, sure

#

that eventually might be an eternity away though

fiery cosmos Nov 11, 2022, 9:54 PM

#

Is my idea for a non deterministic algo accurate or is that not a typical paradigm one might use

haughty mountain Nov 11, 2022, 9:55 PM

#

it's as bad as the deterministic one

#

or worse

fiery cosmos Nov 11, 2022, 9:55 PM

#

I thought non deterministic was just not returning the exact same answer every time is runs. I’m not talking about approximation algos, unless they are synonymous

#

Is non a non deterministic algorithm synonymous with an approximation algorithm?

#

Wikipedia didn’t seem to indicate that

haughty mountain Nov 11, 2022, 9:57 PM

#

it's not synonymous

fiery cosmos Nov 11, 2022, 9:58 PM

#

they're surely related somehow, i would presume

haughty mountain Nov 11, 2022, 9:58 PM

#

but your scheme of keeping the minimum makes it some kind of approximation scheme

fiery cosmos Nov 11, 2022, 9:58 PM

#

what might a typical non-deterministic paradigm look like? i'm happy if you just provide a link to a known algo

haughty mountain Nov 11, 2022, 9:59 PM

#

there is an interesting one, I just need to remember which one it is...

fiery cosmos Nov 11, 2022, 10:00 PM

#

ok ok. my mind just went the approximation route apparently after reading the chapter. book didn't discuss deterministic vs non-deterministic, unless i missed it. i'll check the index

haughty mountain Nov 11, 2022, 10:13 PM

#

I think it's this, but the wiki is probably to hard to read

#

https://en.wikipedia.org/wiki/Karger's_algorithm

Karger%27s_algorithm

#

this is an algorithm that gets the correct answer with a not too low probability

#

so if you repeat it enough times you can be increasingly certain about the correctness of your answer

#

I tool this course years back, the only reason I found what I was thinking of http://www.cse.chalmers.se/edu/year/2018/course/TDA251/

smoky dew Nov 11, 2022, 10:34 PM

#

say I have a class A whose objects each hold unique identifiers x y and z, what would be the right data structure to be able to get the objects from either one of these identifiers? a dict would work if they only had a single identifier but not with multiple, and a list would just be inefficient. is there something else?

haughty mountain Nov 11, 2022, 10:56 PM

#

I'm assuming you mean you should be able to get A from one of x, y, z?

#

you could use a dict and map all three to A

#

it won't be too wasteful since you're not storing copies, just references

lethal ore Nov 12, 2022, 4:13 AM

#

With Reinforced Supervised Learning Using Machine Learning On A Closed System With Say Python, Is It Possible To Link My Library From Google Books And Choose Specific Books By Sequence For The AI To Read And Store It In Memory To Go Alongside Training Data For Such A System Later.

split vector Nov 12, 2022, 10:40 AM

#

hey guys, is sorting an array then doing the rest of the algorithm is still a brute force or brute force doesn't include sorting ?

haughty mountain Nov 12, 2022, 10:45 AM

#

brute force is a very generic term

#

you could use it to describe a lot of things

#

when I hear brute force I think "try basically all relevant possibilities"

split vector Nov 12, 2022, 11:08 AM

#

is this a brute force ?

haughty mountain Nov 12, 2022, 11:16 AM

#

the last part looks greedy, but it also looks weird

split vector Nov 12, 2022, 11:16 AM

#

how can I make it a brute force then

agile sundial Nov 12, 2022, 11:16 AM

#

what's the problem statement?

haughty mountain Nov 12, 2022, 11:17 AM

#

wouldn't budget += i.revenue - i.spend be the sensible thing?

agile sundial Nov 12, 2022, 11:17 AM

#

spend could be negative ig

haughty mountain Nov 12, 2022, 11:18 AM

#

I don't think it can be negative

agile sundial Nov 12, 2022, 11:18 AM

#

oh it's just greedy then right. establish as many as you can

split vector Nov 12, 2022, 11:18 AM

#

agile sundial oh it's just greedy then right. establish as many as you can

How can I make it a brute force

haughty mountain Nov 12, 2022, 11:18 AM

#

agile sundial oh it's just greedy then right. establish as many as you can

yes, starting with the cheapest, if it would make profit overall, do it

agile sundial Nov 12, 2022, 11:18 AM

#

sorting works because then you don't have to care about what project you go to next

haughty mountain Nov 12, 2022, 11:19 AM

#

why would you want to make something brute force?

agile sundial Nov 12, 2022, 11:19 AM

#

ah yeah, it's not guaranteed to be profitable (smh being realistic?)

split vector Nov 12, 2022, 11:19 AM

#

haughty mountain why would you want to make something brute force?

it is required

split vector Nov 12, 2022, 11:20 AM

#

split vector it is required

for some reason ..

#

agile sundial Nov 12, 2022, 11:20 AM

#

I guess brute force would just be trying each permutation of the investments to do in order

haughty mountain Nov 12, 2022, 11:20 AM

#

oh wait

#

you get the initial investment back on top of revenue?

split vector Nov 12, 2022, 11:21 AM

#

haughty mountain you get the initial investment back on top of revenue?

Yea

haughty mountain Nov 12, 2022, 11:21 AM

#

if so you just take all you can, starting from the smallest

agile sundial Nov 12, 2022, 11:21 AM

#

oh so you can't lose money

split vector Nov 12, 2022, 11:22 AM

#

no

haughty mountain Nov 12, 2022, 11:22 AM

#

yeah, it makes the problem pretty boring

agile sundial Nov 12, 2022, 11:23 AM

#

that would just be an if statement though right? if it's negative profit, don't do it

haughty mountain Nov 12, 2022, 11:23 AM

#

yes

split vector Nov 12, 2022, 11:25 AM

#

But I need to check back if I got a project revenue

haughty mountain Nov 12, 2022, 11:26 AM

#

agile sundial I guess brute force would just be trying each permutation of the investments to ...

nice, let's turn our sorting + O(n) solution to an O(n!) one 😛

agile sundial Nov 12, 2022, 11:27 AM

#

isn't it n+1 cause you need to loop lol

haughty mountain Nov 12, 2022, 11:27 AM

#

Ω(n!) then

split vector Nov 12, 2022, 11:27 AM

#

btw is this O(n^2) ?

agile sundial Nov 12, 2022, 11:27 AM

#

yeah, because the bubble sort

haughty mountain Nov 12, 2022, 11:27 AM

#

split vector btw is this O(n^2) ?

you're sorting in O(n²) yes

#

the rest of the code is O(n)

#

idk why you would want to do bubble sort though

split vector Nov 12, 2022, 11:29 AM

#

is it possible to do it with out sorting ?

haughty mountain Nov 12, 2022, 11:29 AM

#

haughty mountain idk why you would want to do bubble sort though

rather than the built-in sort, or a more efficient sorting algo

split vector Nov 12, 2022, 11:29 AM

#

haughty mountain rather than the built-in sort, or a more efficient sorting algo

Oh I see

#

that I can do

#

But my problem is

#

I have to write 2 algorithms

#

one is brute force

#

and the other one is any other algorithm with less O( )

#

and when I got this algorithm I dont know if it is a brute force or not 😅

#

this one

haughty mountain Nov 12, 2022, 11:31 AM

#

I don't think you can solve efficiently without sorting, I can construct cases where you need to do things in sorted order to be optimal

#

no, what you have (if we ignore the sorting being written in a slow way) is a very good solution

split vector Nov 12, 2022, 11:33 AM

#

haughty mountain no, what you have (if we ignore the sorting being written in a slow way) is a ve...

I can change the sorting algorithm

haughty mountain Nov 12, 2022, 11:33 AM

#

as said, I don't think you can do it without considering the sorted order somehow, and your second part is O(n) and cheaper than sorting

split vector Nov 12, 2022, 11:34 AM

#

and it is greedy algorithm right ?

haughty mountain Nov 12, 2022, 11:35 AM

#

the very dumb solution that @agile sundial mentioned of considering all permutations of all subsets will eventually consider the sorted version of the thing you need

just insanely inefficiently

haughty mountain Nov 12, 2022, 11:36 AM

#

split vector and it is greedy algorithm right ?

it is, after sorting you greedily pick things if you can

dreamy valley Nov 12, 2022, 11:36 AM

#

split vector this one

are you sure you're solving the right problem there?
because there's no obvious "brute force" version of this one, but if I tweak the parameters a bit it looks like an O(2^n) problem that might have an efficient dynamic programming solution

agile sundial Nov 12, 2022, 11:36 AM

#

haughty mountain the very dumb solution that <@182894631921516545> mentioned of considering all p...

but it's brute force!

haughty mountain Nov 12, 2022, 11:36 AM

#

brute factorial

split vector Nov 12, 2022, 11:37 AM

#

dreamy valley are you sure you're solving the right problem there? because there's no obvious ...

yea

haughty mountain Nov 12, 2022, 11:38 AM

#

dreamy valley are you sure you're solving the right problem there? because there's no obvious ...

sorting+greedy is the best you can do

split vector Nov 12, 2022, 11:39 AM

#

so for the 2 algorithm the brute force one is the one @agile sundial mentioned, and mine is a greedy algorithm yea ?

haughty mountain Nov 12, 2022, 11:41 AM

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well, asking for a brute force one here is just weird

dreamy valley Nov 12, 2022, 11:41 AM

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that's why I'm wondering if the problem is specified wrong

haughty mountain Nov 12, 2022, 11:42 AM

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there is no obvious brute force algo here

split vector Nov 12, 2022, 11:42 AM

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I guess our tutor hates us then

haughty mountain Nov 12, 2022, 11:42 AM

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I think any brute force algo will use basically the second loop you have

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because you need to check if the investment is valid

dreamy valley Nov 12, 2022, 11:44 AM

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I was thinking of the case where you have n investments that you have to make simultaneously and you have to optimize your return in one investment cycle. The fact that you can get the return from investment A before you have to invest in B is what makes sorting+greedy work here

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but that does seem to be what the poorly written explanation is saying so 🤷‍♂️

haughty mountain Nov 12, 2022, 11:45 AM

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dreamy valley I was thinking of the case where you have n investments that you have to make si...

the second example shows that's the case

dreamy valley Nov 12, 2022, 11:45 AM

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yeah I was just having a hard time reading it

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still weird to ask for a brute force algorithm

haughty mountain Nov 12, 2022, 11:46 AM

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it is

split vector Nov 12, 2022, 11:46 AM

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what I can adjust to it to make it a brute force i didn't get

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how the code will be

haughty mountain Nov 12, 2022, 11:47 AM

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in a bunch of cases there is some obvious but inefficient brute force, this is not one of these cases