代码

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

评测结果