从有序数组中查找某个值

int n, k;
void solve()
{
	int lb = -1, ub = n;
	//重复循环，直到解的存在范围不大于1
	while (ub - lb  > 1) {
		int mid = (lb + ub) / 2;
		if (a[mid] >= k) {
			//若果mid满足条件，则解的存在范围变为（lb, mid]
			ub = mid;
		} else {
		//如果mid不满足条件，则解的存在条件变为（mid, ub]
		lb = mid;
		}
	}
	//这时, lb + 1 = ub;
	printf("%d\n", ub);
}