快速排序（模板）

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 1000010;
int a[N];
int n;
int read()
{
    int f = 1 , s = 0;
    char c = getchar();
    while(c > '9' || c < '0') {if(c == '-') f = -1 ;c = getchar();}
    while(c >='0' && c <= '9') s = s * 10 + c - '0' , c = getchar();
    return s * f;
}
void quick_sort(int a[] , int l , int r)
{
    if(l >= r) return;
    int i = l - 1 , j = r + 1;
    int x = a[l + r >> 1];
    // cout << i << " " << j << endl;
    while(i < j)
    {
        do i ++ ; while(a[i] < x);
        do j -- ; while(a[j] > x);
        if(i < j) swap(a[i] , a[j]);
    }
    quick_sort(a , l , j);
    quick_sort(a , j + 1 , r);
}
int main()
{
    cin >> n;
    for(int i = 0 ; i < n ; i ++)
        a[i] = read();
    quick_sort(a , 0 , n - 1);
    // cout << a[0];
    for(int i = 0 ; i < n ; i ++ ) cout << a[i] <<" ";
}