题目：
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].
Note:
You must do this
in-place without making a copy of the array.Minimize the total number of operations.
思路：
好简洁的代码呀！注意理解k的含义。
代码：
class Solution {
public:
void moveZeroes(vector<int>& nums) {
for(int i = 0, k = 0; i < nums.size(); ++i) {
if(nums[i] != 0) {
swap(nums[i], nums[k++]);
}
}
}
};
