题解 | #寻找第K大#

思路

借助快排的Partition函数
注意：
1、是第K大，因此Partition返回的结果要和n-K比较！！！

代码

class Solution {
public:

    int Partition(vector<int>& arr, int L, int R ){
        int right = R;
        int left = L;
        int key = arr[left];

        while(left< right){
            while(left< right && arr[right]>=key){
                right--;
            }
            arr[left] = arr[right];

            while(left< right && arr[left]<=key){
                left++;
            }
            arr[right] = arr[left];
        }

        arr[left] = key;
        return left;

    }

    int findKth(vector<int> a, int n, int K) {
        // write code here
        int start = 0;
        int end = n-1;
        int index = Partition(a, start, end);
        while(index!=n-K){
            if(index<n-K){
                start = index+1;
                index = Partition(a, start, end);
            }
            else{
                end = index-1;
                index = Partition(a,start, end);
            }
        }

        return a[index];

    }
};