#HOW TO CHECK PRIME NUMBER WITHOUT LOOP?

57 messages · Page 1 of 1 (latest)

crimson hollow
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How to check prime number just by using if else statement?

marsh coveBOT
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west plinth
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if you have an infinikeyboard you could type

if (x == 1 && x == 2 && x == 3 && x == 5 && x = 7 && .......
.........
.............
...................
) {
   ... x is prime ...
}
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you would just have to type all of the prime numbers

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pretty sure they havent proved there is infinite prime numbers yet so you could probably use a regular keyboard but an infinikeyboard makes it easier

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(truthfully, loop is probably the best way to check for prime :D)

wide jolt
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If there was finitely many, let's say k prime numbers, then what about (P1*P2*P3...*Pk)+1?

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On a side note, there are some relatively quick primarily tests for numbers < 2^64 (fitting into unsigned long long)

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Most important being Miller Rabin test

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In your case that's likely not what you are looking for

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Create a function is_prime returning bool, that checks that the number has no divisors, then do if (is_prime(n)) ...

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To get the "just an if" semantics

exotic basin
exotic basin
broken snow
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is recursion allowed?

exotic basin
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if your integer is 64 bits then in principle you have to check all possible prime divisors up to 2^32, and by the prime number theorem, there are approximately 2^32 / ln(2^32) = 1.9364e8 such primes, so the naive solution is gonna take a while

rough lodge
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you could use Wilsons theorem and the gamma function in the stl to avoid using a loop for factorial but you're gonna run out of digits rather quickly

broken snow
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don't they use loops?

wide jolt
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You can use MR test for like 9 bases in ifs :p but still there are loops under the hood for fast power

rough lodge
broken snow
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slightly off topic, but if you pre-compute E = 2 * 3 * 5 ... N - 1, where N = P * Q, then divide E by N, couldn't you binary search the missing prime numbers in the composite by precomputed sub-products of E / N?

rough sleet
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oh, look at me, contributing nothing helpful to the conversation...

broken snow
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the proof is quite elegant

broken snow
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euclid showed it BC

rough sleet
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you are right

rough sleet
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i love math proofs

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but we're beyond the point of the question :-/

broken snow
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i mean the question is kind of nonsensical / ambiguous so what would you expect

rough sleet
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true

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im glad i'm no longer in school

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actually, i lie. i liked the wonky stuff like this they gave. in real life, it's much less fun

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in any case, i know very little cpp so im not a good influence lol

late eagle
exotic basin
broken snow
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how would you store it and make lookups?

exotic basin
broken snow
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yeah just slap a buzzword on it

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hey, we could make an AI

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using quantum computing and TPUs (buzzword in 3-5 years) to power high performance cloud computing on-prem

west plinth
west plinth
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i guess my point is that it shouldnt be done this way

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i figure that kinda got across

exotic basin
late eagle
obsidian cloud
broken oriole
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To answer, the most likely answer whatever this assignment is asking for is using recursion, you can write a naive one with using a helper function that takes the number and current divisor to check and return a bool

thorny jasper
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You can use sieve up to number and then check if the number is in the sieve

wide jolt
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Oh oh i know! You can use my library!

fierce kraken
wide jolt
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Mhmm

marsh coveBOT
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