二分查找模板

#include <iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=10000+5;
int a[maxn];
//非递归实现
int binary_search(int left,int right,int n)                    //返回索引值，如果未查找到则返回-1
{
    while(left<right)
    {
        int mid=left+(right-left)/2;
        if(n==a[mid]) return mid;
        if(n<a[mid]) right=mid;
        if(n>a[mid]) left=mid+1;
    }
    if(left==right)
    {
        if(a[left]==n) return left;
    }
    return -1;
}
//递归实现
int binary_search(int left,int right,int n)
{
    if(left==right) {
                            if(a[left]==n) return left;
                            return -1;
                           }
    int mid=left+(right-left)/2;
    if(a[mid]==n) return mid;
    if(a[mid]>n) binary_search(left,mid,n);
    else if(a[mid]<n) binary_search(mid+1,right,n);
}
int main()
{
    int n,m;                            //n为数组大小，m为询问次数
    while(scanf("%d%d",&n,&m)==2&&n)
    {
        for(int i=0;i<n;i++)
            scanf("%d",&a[i]);
        sort(a,a+n);
        while(m--)
        {
            int k;
            scanf("%d",&k);
            int b=binary_search(0,n,k);               //左闭右开的区间
            printf("%d\n",b);
        }
    }
    return 0;
}