分治法寻找第k大的数

利用快速排序的思想·去做

#include<iostream>
using namespace std;
int FindKthMax(int*list, int left, int right, int k);
int main(){
int i,n,k;
while (cin >> n){
int *a = new int[n];
for (i = 0; i < n; i++)
cin >> a[i];
cin >> k;
cout << FindKthMax(a, 0, n - 1, k) << endl;
}
return 0;
}
int FindKthMax(int*list, int left, int right, int k){
int key = list[left];
int low = left, high = right;
while (low < high){
while (list[high]>=key&&high > low)
high--;
list[low] = list[high];
while (list[low]<=key&&high>low)
low++;
list[high] = list[low];
}
list[low] = key;
/*实现一次快速排序*/
int l = right - low + 1;
if (l == k) //若key处恰好为第k大数，直接返回
return key;
else if (l < k)
/*l<k说明第k大数在key左边序列中，此时为第k-l大的数*/
FindKthMax(list, left, low - 1, k - l);
else
/*l>k说明第k大的数在右边序列中，位置还是第k大的数*/
FindKthMax(list, low + 1, right, k);
}