Given an array of numbers (1,2,3,8,0,2,2,0,10), move all 0s to the right end and all other numbers to the left while keeping relative order of non-zero numbers. Has to be linear in time and in-place.

separate_zeroes.py

def separate_zeroes(nums):
    '''
    Given an array of numbers (1,2,3,8,0,2,2,0,10), move all 0s to the right end and all other numbers to the left while keeping relative order of non-zero numbers. Has to be linear in time and in-place.
    
    >>> separate_zeroes([1, 2, 3, 8, 0, 2, 2, 0, 10])
    [1, 2, 3, 8, 2, 2, 10, 0, 0]

    >>> separate_zeroes([1, 1, 1, 0, 1, 0, 0, 1])
    [1, 1, 1, 1, 1, 0, 0, 0]

    >>> separate_zeroes([0])
    [0]

    >>> separate_zeroes([0, 0, 1])
    [1, 0, 0]

    >>> separate_zeroes([0, 0, 0, 1, 0, 0, 0])
    [1, 0, 0, 0, 0, 0, 0]

    '''
    num_zeroes = 0
    zero_to_swap = None

    for i in range(0, len(nums)):
        if nums[i] == 0:
            if zero_to_swap is None:
                zero_to_swap = i
        else:
            if zero_to_swap is not None:
                nums[zero_to_swap] = nums[i]
                nums[i] = 0
                zero_to_swap = i

    return nums


if __name__ == '__main__':
    import doctest
    doctest.testmod()