快速排序

思路很简单 找一个基数，让左边的小于等于基数，右边的大于等于基数

#include <cstdio>
#include <iostream>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <cstring>
#include <string>
#include <sstream>
#include <cmath>
#include <cstdlib>
#include <algorithm>

#define sf scanf
#define pf printf
#define fp(x) freopen((x), "r", stdin)

typedef long long ll;

using namespace std;

void pri1(int arr[], int start, int end)
{
    while (start<=end) pf("%d ", arr[start++]);
    pf("
");
}

void pri2(int **arr, int start1, int end1, int start2, int end2)
{
    for (int i=start1; i<=end1; i++) {
        for (int j=start2; j<=end2; ++j) {
            pf("%d ", arr[i][j]);
        }
        pf("
");
    } 
}

void _qsort(int arr[], int left, int right) // 下标[a,b]
{
    if (left >= right) return ;
    int tmp,i,j,tt;
    
    tmp = arr[(left+right)/2]; //实现“随机取基数” 
    arr[(left+right)/2] = arr[left];
    arr[left] = tmp;
    
    i = left;
    j = right;
    while (i < j) {
        while (i < j && tmp <arr[j]) j--;
        while (i < j && tmp>=arr[i]) i++;
        if (i < j) {
            tt = arr[i];
            arr[i] = arr[j];
            arr[j] = tt;
        } 
    }
    arr[left] = arr[i];
    arr[i] = tmp;
    _qsort(arr, left, i-1);
    _qsort(arr, i+1, right);
} 

int main()
{
//    int arr[] = {1, 8, 11, 5, 9, 2, 4, 6, 77, 111};
//    int arr[] = {1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
//    int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
//    int arr[] = {10, 9, 8, 7, 6, 5, 4, 3, 2, 1};
//    int arr[] = {1, 2, 1, 2, 1, 1, 1, 1, 1, 1};
//     int arr[] = {1, 2, 1, 1, 1, 1, 1, 1, 1, 1};
    _qsort(arr, 0, 9);    
    pri1(arr, 0, 9);

    return 0;
}