'''
Given an array nums, write a function to move all 0's to the end of it while maintaining the relative order of the non-zero elements.

For example, given nums = [0, 1, 0, 3, 12], after calling your function, nums should be [1, 3, 12, 0, 0].

20 minutes

1 1 0 3 12
^
    ^
0 1 1 3 12
  ^
      ^

0 0 1 4 2 5
    ^
  ^
0 0 1 4 0 5
    ^
  ^
'''