移动零

 由删除排序数组中的重复项来的灵感，都是交换类题目，双指针，k之前的都是有效位

class Solution:
    def moveZeroes(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        if nums:
            k = 0
            
            for i, num in enumerate(nums):
                if num != 0:
                    #遇到不等于0的就交换，然后k+1
                    t = nums[k]
                    nums[k] = num
                    nums[i] = t
                    k += 1