二分查找的两种正确实现

#include <iostream>
using namespace std;

int binarySearch1(int a[], int n, int x)  //[l, u)区间
{  
    int l, u, m;  
    l = 0;  //左区间闭合
    u = n;  //右区间开放 
    while(l < u)  //用<做判断，不用<=
    {  
        m = l + ( (u-l) >> 1);  //防止加法(l + u)溢出，不能写成 m = (l + u) / 2;
        if(x < a[m])  
            u = m;  //因为右区间是开放的，所以右边不用-1
        else if(x == a[m])  
            return m;  
        else  
            l = m + 1;  
    }  
    return -1;  
}  

int binarySearch2(int a[], int n, int x)  //[l, u]区间
{  
    int l, u, m;  
    l = 0;  //左区间闭合
    u = n - 1;  //右区间闭合 
    while(l <= u)  //用<=做判断，不用<
    {  
        m = l + ( (u-l) >> 1);  //防止加法(l + u)溢出，不能写成 m = (l + u) / 2;
        if(x < a[m])  
            u = m - 1;  //因为右区间是闭合的，所以右边要-1
        else if(x == a[m])  
            return m;  
        else  
            l = m + 1;  
    }  
    return -1;  
}  


int main()
{
    int a[5] = {1, 2, 7, 4, 3};
    cout << binarySearch1(a, 5, 7) << " " << binarySearch2(a, 5, 7) << endl;
    getchar();
    return 0;
}