# 快速排序算法总结（例题：第k个数）

#include <iostream>

using namespace std;

const int N = 1e5 + 10;

int n;
int q[N];

void quick_sort(int q[], int l, int r)
{
if (l >= r) return;

int x = q[(l + r) / 2], i = l - 1, j = r + 1;
while (i < j)
{
do i++; while (q[i] < x);
do j--; while (q[j] > x);
if (i < j) swap(q[i], q[j]);
}

quick_sort(q, l, j);
quick_sort(q, j + 1, r);
}

int main()
{
scanf("%d", &n);
for (int i = 0; i < n; i++) scanf("%d", &q[i]);

quick_sort(q, 0, n - 1);

for (int i = 0; i < n; i++) printf("%d ", q[i]);

return 0;
}

https://www.acwing.com/problem/content/788/

#include <iostream>

using namespace std;

const int N = 1e5 + 10;

int n, k;
int q[N];

int quick_sort(int l, int r, int k)
{
if (l == r) return q[l];

int x = q[l], i = l - 1, j = r + 1;
while (i < j)
{
while (q[++i] < x);
while (q[--j] > x);
if (i < j) swap(q[i], q[j]);
}

int sl = j - l + 1;
if (k <= sl) return quick_sort(l, j, k);

return quick_sort(j + 1, r, k - sl);
}

int main()
{
cin >> n >> k;

for (int i = 0; i < n; i++) cin >> q[i];

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

return 0;
}

posted @ 2023-11-19 23:48  ykycode  阅读(8)  评论(0编辑  收藏  举报