二分查找

非递归

 

#include <iostream>
#include<cstdlib>
#include<cstring>
using namespace std;


int bin_search(int a[],int low,int high,int des){
    int mid;
    if(a!=NULL&&(low<high)){
    while(low<=high){
            mid=(low+high)/2;
        if(a[mid]==des){
            return mid;
        }
        else if(a[mid]>des){
            high=mid-1;
        }
        else
            low=mid+1;
        }
    }
    return -1;
}

int main()
{
    int a[]={1,2,3,4,5,6,7,8,9};
    int low=0;
    int high=sizeof(a)/sizeof(*a)-1;
    cout<<bin_search(a,low,high,5);
    return 0;
}

递归

#include <iostream>
#include<cstdlib>
#include<cstring>
using namespace std;


int bin_search(int a[],int low,int high,int des){
    int mid;
    if(a!=NULL&&(low<high)){
    while(low<=high){
            mid=(low+high)/2;
        if(a[mid]==des){
            return mid;
        }
        else if(a[mid]>des){
            high=mid-1;
        }
        else
            low=mid+1;
        }
    }
    return -1;
}

int main()
{
    int a[]={1,2,3,4,5,6,7,8,9};
    int low=0;
    int high=sizeof(a)/sizeof(*a)-1;
    cout<<bin_search(a,low,high,5);
    return 0;
}