三种方法实现二分查找

最近打算研究一下基础的算法，就先从二分开始做吧，三种方法

#include <bits/stdc++.h>
using namespace std;

const int MAXN = 1024;
int num[MAXN];

//生成测试数据
void init()
{
    for(int i = 0; i < MAXN; i++)
        num[i] = i * 3;
}

//循环查找
int query1(int n)
{
    int l = 0, r = MAXN;
    while(l <= r){
        int mid = (l + r) >> 1;
        if(num[mid]==n) return mid;
        else if(num[mid]<n) l = mid + 1;
        else r = mid - 1;
    }
    return -1;
}

//递归查找
int query2(int l, int r, int n)
{
    if(l > r) return -1;
    int mid = (l + r) >> 1;
    if(num[mid]==n) return mid;
    else if(num[mid] < n) return query2(mid + 1, r, n);
    else return query2(l, mid-1, n);
}

//STL查找
int query3(int n)
{
    if(!binary_search(num, num+MAXN, n))
        return -1;
    return  lower_bound(num, num+MAXN, n) - num;
}

void run()
{
    int n;
    printf("
输入要查找的数：");
    cin >> n;
    printf("%d 的下标为:
", n); //输出-1为不存在
    cout << "循环查找：" << query1(n) << endl;
    cout << "递归查找：" << query2(0, MAXN, n) << endl;
    cout << "STL查找：" << query3(n) << endl;
    run();
}

int main()
{
    init();
    run();
    return 0;
}