shifting elements of list to the left by the specified shift amount in python

Question

how to create a function that copies every value in the original list to a new list where the position of every value in the new list is shifted to the left by the specified shift amount

e.g. [2,3,4,5] woule become [4,5,2,3]

How can I create this function WITHOUT using any builtin functions?

by any builtin function do you mean cannot use builtin function neither like append nor pop at all ? — humphrey chan, Nov 02 '22 at 07:04
Hello, I think this post might help: https://stackoverflow.com/questions/2150108/efficient-way-to-rotate-a-list-in-python — Swifty, Nov 02 '22 at 09:07
Please provide enough code so others can better understand or reproduce the problem. — Community, Nov 02 '22 at 12:57

score 0 · Answer 1 · answered Nov 02 '22 at 07:04

Solution

a = [2, 3, 4, 5]


def shift_left(arr: list, amount: int) -> list:
    amount %= len(arr)  # (1)
    return arr[amount:] + arr[:amount]  # (2)


for i in range(len(a) * -2, len(a) * 2):
    print(i, shift_left(a, i))

output:

-8 [2, 3, 4, 5]
-7 [3, 4, 5, 2]
-6 [4, 5, 2, 3]
-5 [5, 2, 3, 4]
-4 [2, 3, 4, 5]
-3 [3, 4, 5, 2]
-2 [4, 5, 2, 3]
-1 [5, 2, 3, 4]
0 [2, 3, 4, 5]
1 [3, 4, 5, 2]
2 [4, 5, 2, 3]
3 [5, 2, 3, 4]
4 [2, 3, 4, 5]
5 [3, 4, 5, 2]
6 [4, 5, 2, 3]
7 [5, 2, 3, 4]

Explanation

amount %= len(arr): normalize the amount within length of the array.
arr[amount:] + arr[:amount]: slice the array into two parts and concatenate it.

shifting elements of list to the left by the specified shift amount in python

1 Answers1

Solution

Explanation