Problem: Move given elements to the end of the list

You are given an array of integers and an integer. Write a function that moves all the instances of that integer in the array to the end of the array.

Sample input:

[2, 1, 2, 3, 7, 2, 1], 2

Sample output:

    [1, 3, 7, 1, 2, 2, 2]

def move_elements_to_end(array, to_move):
    """O(n) time | O(1) space, since we aren't using any auxiliary data structure."""
    
    i = 0
    j = len(array) - 1

    while i < j:
        while i < j and array[j] == to_move:
            # decrement j to point to an integer that isn't  to_move
            j -= 1

        if array[i] == to_move:
            # swap (constant time operation)
            array[i], array[j] = array[j], array[i]

        # increment i
        i += 1

    return array

move_elements_to_end([2, 1, 2, 3, 7, 2, 1], 2)

[1, 1, 7, 3, 2, 2, 2]