240. Search a 2D Matrix II

class Solution {
public:
    bool searchMatrix(vector<vector<int>>& matrix, int target) {
        int m = matrix.size(), n = m ? matrix[0].size() : 0;
        int i = 0, j = n - 1;
        while (i < m) {
            while (j >= 0 && matrix[i][j] > target) j--;
            if (j < 0) return false;
            if (matrix[i][j] == target) return true;
            i++;
        }
        return false;
    }
};