two pointers(加复习)

fill(nums.start()+?, nums.end(), 0)
nums.insert(nums.begin()+?, 0)

快速排序
判断left 和 right大小使用<=, pivot 使用小于

class Solution {
public:
    vector<int> sortArray(vector<int>& nums) {
        helper(nums, 0, nums.size()-1);
        return nums;
    }


    void helper(vector <int> & nums, int start, int end){
        if (start >= end){
            return;
        }
        int left = start, right = end ;
        int pivot = nums[int((left + right)/2)];
        while (left <= right){            
            while(left <= right && nums[left] < pivot){
                left += 1;
            }
            while(left <= right && nums[right] > pivot ){
                right -= 1;
            }
            if (left <= right){
                int temp = nums[left];
                nums[left] = nums[right];
                nums[right] = temp;
                left ++;
                right --;
            }
        }
        helper(nums, start, right);
        helper(nums, left, end);
    }


};