🔒 recursion not working as intended

[spiral juniper]

taking a list of integers and duplicating all elements in it while keeping order; no auxiliary structures available
eg: [1,2,3,] becomes [1,1,2,2,3,3]
this is my approach:

def stutter_list(lst):
    if not lst:
        return
    tmp = lst.pop()
    lst.append(tmp)
    lst.append(tmp)
    stutter_list(lst[:-2])```
im thinking i pop the last element in the list, append it twice because the goal is change the parameter of the list given(would the verb for mutable be mutate), and then recursively call the function without the last two elements

[spare jasper]

@spiral juniper

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[regal portal]

lst[:-2] will make a copy of the list

so when the recursive calls make edits to lst[:-2], they are not editing the orignal list

try

def stutter_list(lst):
    if not lst:
        return
    tmp = lst.pop()
    stutter_list(lst[:-2])
    lst.append(tmp)
    lst.append(tmp)

[spiral juniper]

doesnt seem to work, same output

if lst[:-2] makes a copy of the lst i probably cant use it though(?)

[spare jasper]

:white_check_mark: Your 3.12 eval job has completed with return code 0.

None

[vagrant owl]

!e

def stutter_list(lst):
    if not lst:
        return
    tmp = lst.pop()
    lst.append(tmp)
    lst.append(tmp)
    stutter_list(lst[:-2])
a = [1,2,3]
stutter_list([1,2,3])
print(a)```

[spare jasper]

:white_check_mark: Your 3.12 eval job has completed with return code 0.

[1, 2, 3]

[sand whale]

this can be simplified a lot more:

!e

def stutter(list):
  if not list:
    return []
  return [list[0], list[0]] + stutter(list[1:])

print(stutter([1, 2, 3]))

[spare jasper]

:white_check_mark: Your 3.12 eval job has completed with return code 0.

[1, 1, 2, 2, 3, 3]

[sand whale]

unless it must be mutating in place?

[vagrant owl]

why was the original not working?

[sand whale]

is this what you are referring to as "original"? @vagrant owl

[vagrant owl]

yes

[spiral juniper]

im not sure what mutating in place means, i would like to mutate the parameter that was passed

[sand whale]

ah yeah, that is in-place

[spiral juniper]

testing this and im getting a max recursion depth error

also i think that returns a new list(?)

[spare jasper]

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