代码

int binary_search(const unsigned *a, int n, unsigned x)
{
    int l=-1,r=n;
    while(l+1<r)
    {
        int mid = (l+r)/2;
        if(a[mid]>n)
        {
             r=mid;
        }
        else //if(a[mid]<n)
        {
             l=mid;
        }
/*
        else
        {
             return mid;
        }*/
    }
    return l-1;
}

评测结果