快排实现；

1：用递归；(left<right)为进入条件

2：两边逼近:（low<high）-》先右边找到不满足的放到左边的（无意义位）空位置中，通过这个循环后就可以逼近low=high，这时把目标key付给v[low]，即最后一个空位也填满了

 

 

#include <iostream>
  2 #include <vector>
  3 using namespace std;
  4 void quicksort(int *v, int left, int right){
  5         if(left < right){
  6                 int key = v[left];
  7                 int low = left;
  8                 int high = right;
  9                 while(low < high){
 10                         while(low < high && v[high] >= key){
 11                                 high--;
 12                         }
 13                         v[low] = v[high];
 14                         while(low < high && v[low] <= key){
 15                                 low++;
 16                         }
 17                         v[high] = v[low];
 18                 }
 19                 v[low] = key;
 20                 quicksort(v,left,low-1);
 21                 quicksort(v,low+1,right);
 22         }
 23 }
 24 int main(){
 25     int ivec[5];
 26     int ic;
 27     for(int ix=0;ix!=5;++ix)
 28     {
 29           cin>>ic;
 30           ivec[ix]=ic;
 31     }
 32      for(int ix=0;ix!=5;ix++)
 33         cout<<ivec[ix]<<" ";
 34         cout<<"\n";
 35     quicksort(ivec,0,4);
 36     for(int ix=0;ix!=5;ix++)
 37         cout<<ivec[ix]<<" ";
 38 return 0;
 39 }