快排实现时候的一个逻辑错误

　

#include"header_file.h"
using namespace std;

void swap(int a,int b)
{
    int t;
    t=a;
    a=b;
    b=t;
}

void quick_sort(int a[],int low,int high)
{
    
    if(low>=high)
        return;
        
    int first;
    int last;
    first=low;
    last=high;
    
    int x;
    x=a[low];
    

    while(low<high)
    {
        while(low<high&&a[high]>=x)
        {
            high--;
        }    
        swap(a[low],a[high]);
        
        cout<<i<<"      "<<low<<" low"<<"  "<<high<<endl;
        
        while(low<high&&a[low]<=x)
        {
            low++;
        }
        swap(a[high],a[low]);
        cout<<i<<"      "<<low<<" high"<<"  "<<high<<endl;
    }
    if(first<low-1)
        quick_sort(a,first,low-1);
    if(last>low+1)
        quick_sort(a,low+1,last);
}

int main(void)
{
    int a[7]={4,3,6,7,2,1,5};
    quick_sort(a,0, sizeof(a) / sizeof(a[0]) - 1);
    
    cout<<"test"<<endl;
    for(int i=0;i<7;i++)
        cout<<a[i]<<" ";
}

执行程序会发现在算法排序的地方无限循环，想了半天才知道是33和41行的位置，不管while循环是否执行都会执行swap语句。逻辑错误！

只能换种方法，改成大家最常见的那种就好了

void quick_sort(int a[],int low,int high)
{
    
    if(low>=high)
        return;
        
    int first;
    int last;
    first=low;
    last=high;
    
    int x;
    x=a[low];
    

    while(low<high)
    {
        while(low<high&&a[high]>=x)
        {
            high--;
        }    
        a[low]=a[high];
        
    //    cout<<i<<"      "<<low<<" low"<<"  "<<high<<endl;
        
        while(low<high&&a[low]<=x)
        {
            low++;
        }
        a[high]=a[low];
    //    swap(a[high],a[low]);
    //    cout<<i<<"      "<<low<<" high"<<"  "<<high<<endl;
    }
    a[low]=x;
    
    if(first<low-1)
        quick_sort(a,first,low-1);
    if(last>low+1)
        quick_sort(a,low+1,last);
}

这里就不是交换了，直接赋值，然后最后给a[low]赋值。

很低级的错误