下面LIS函数试图求出最长上升子序列的长度，其时间复杂度为（ ）。
#define INT_MIN (-1000)int LIS(vector<int> & nums) { int n = nums.size(); vector<int> tail; tail.push_back(INT_MIN); for (int i = 0; i < n; i++) { int x = nums[i], l = 0, r = tail.size(); while (l < r) { int mid = (l + r) / 2; if (tail[mid] < x) l = mid + 1; else r = mid; } if (r == tail.size()) tail.push_back(x); else tail[r] = x; } return tail.size() - 1;}