二分查找算法

 

#include<iostream>
#include<stdio.h>
using namespace std;

const int MAXN=1024;

int bin_search(int a[], int len, int goal){//二分查找
    int low,high,mid;
    low=0;
    high=len-1;

    while(low<=high){
        mid=(high-low)/2+low;//直接使用(high+low)/2可能导致溢出

        if(goal==a[mid]){
            return mid;
        }
        else if(goal<a[mid]){//在左半边
            high=mid-1;
        }
        else{//在右半边
            low=mid+1;
        }
    }

    return -1;//没找到
}

int main(){
    int a[MAXN];
    int i;
    int index;
    int goal;

    for (i=0;i<MAXN;++i){
        a[i]=i;
    }

    goal=500;
    index=bin_search(a,MAXN,goal);//找goal这个数
    if(index!=-1){
        printf("%d's index:%d\n",goal,index);
    }
    else{
        printf("not found!\n");
    }
    return 0;
}