#include<iostream>
#include<cstdio>
using namespace std;
void swap(int arr[], int i, int j){
    int t=arr[i];
    arr[i]=arr[j];
    arr[j]=t;
}
int partition(int arr[], int low, int end){
   int i=low;
   int j=end+1;
   int x=arr[low];
   while (1){
     while (i<end&&arr[++i]<x);
     
 
while (arr[--j]>x);
     if (i>=j) break;
     swap(arr, i, j);
   }
   swap(arr, low, j);
   return j;
}
void quicksort(int arr[],int low,int high){
   if (low<high){
    int p=partition(arr, low, high);
    quicksort(arr, low, p-1);
    quicksort(arr,p+1, high);
    }
}
int main(){
    int
 
 arr[6] = {23,1,21, 21,4,19};
    quicksort(arr,0,5);
    for(int i=0;i<6;i++){
        printf("%d ",arr[i]);
    }
    printf("\n");
}

排序算法<三>快速排序