C++ 代码

#include<iostream>
using namespace std;
const int N = 1e5 + 10;
int ans[N];

int quickselect(int l, int r, int k) {
    if (l == r) return ans[l];
    int i = l - 1, j = r + 1, tmp = ans[l];
    while (i < j) {
        while (ans[++i] < tmp);
        while (ans[--j] > tmp);
        if (i < j) swap(ans[i], ans[j]);
    }
    int cnt = j - l + 1;
    if (cnt >= k) return quickselect(l, j, k);
    return quickselect(j + 1, r, k - cnt);
}

int main()
{
    int n, k;
    cin >> n >> k;
    for (int i = 0; i < n; ++i) cin >> ans[i];

    cout << quickselect(0, n - 1, k) << endl;

    return 0;
}