代码

int binary_search(const unsigned *a, int n, unsigned x)
{
    int l=0,r=n-1,mid;
    while(l<=r){
        mid=(l+r)>>1;
        if(a[mid]<=x){
            l=mid+1;
        }else{
            r=mid-1;
        }
    }
    return l-1;
}

评测结果