283. move zeroes

Given an integer array nums, move all 0’s to the end of it while maintaining the relative order of the non-zero elements.

Note that you must do this in-place without making a copy of the array.

solution

We use a two pointers strategy to swap zeroes to the back of the array. Keep track of where the leftmost zero is, and where the leftmost nonzero that is to the right of a zero is.

def moveZeroes(self, nums: List[int]) -> None:
	n = len(nums)
	z = 0
	  
	# advance z to first 0
	while z < n and nums[z] != 0:
		z += 1
	  
	v = z
	# advance v to first non-0
	while v < n and nums[v] == 0:
		v += 1
	  
	while z < n and v < n:
		nums[z], nums[v] = nums[v], nums[z]
	  
		while z < n and nums[z] != 0:
			z += 1
		while v < n and nums[v] == 0:
			v += 1