1351. Count Negative Numbers in a Sorted Matrix

class Solution {
public:
    int countNegatives(vector<vector<int>>& grid) {
        int m = grid.size();
        int n = grid[0].size();
        int i=0, j = 0, cnt = 0;
        while( i < m)
        {
            if(grid[i][j] < 0)
            {
                cnt++;
            }

            if(j < n-1)
                  j+=1;
            else
            {
                  i+=1;
                  j = 0;
            }
               
        }
        return cnt;
        
    }
};