215. Kth Largest Element in an Array 第K大的数

class Solution {
public:
    int quicksort(vector<int>& nums, int start, int end, int k){
        int i = start;
        int j = end;
        int x = nums[i];
        while (i<j){            //快排核心…
            while (nums[j]<x && i<j)
                j--;
            if (i<j)
                nums[i++] = nums[j];
            while (nums[i]>x && i<j)
                i++;
            if (i<j)
                nums[j--]=nums[i];
        }
        nums[i] = x;
        if (i==k-1) return x;
        else if (i>k-1)         //出错的地方……………………
            return quicksort(nums,start,i-1,k);
        else
            return quicksort(nums,i+1,end,k);
    }
public:
    int findKthLargest(vector<int>& nums, int k) {
        int len = nums.size();
        //思路：快排，从大到小，放在第（K-1）处的就是第k大的
        int res = quicksort(nums,0,len-1,k);
        return res;
    }
};