代码

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

评测结果