Count Negative Numbers in a Sorted Matrix

class Solution {
public:
    int countNegatives(vector<vector<int>>& grid) {
        int ans = 0;
        for (auto u : grid) {
            reverse(u.begin(), u.end());
            ans += lower_bound(u.begin(), u.end(), 0) - u.begin();
        }
        return ans;
    }
};