Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

Integers in each row are sorted from left to right.
The first integer of each row is greater than the last integer of the previous row.
Example 1:

Input:
matrix = [
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]
target = 3
Output: true
Example 2:

Input:
matrix = [
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]
target = 13
Output: false

public boolean searchMatrix(int[][] matrix, int target) {
        if(matrix == null || matrix.length == 0 || matrix[0].length == 0) return false;
        int row = matrix.length;
        int col = matrix[0].length;
        int l = 0;
        int r = row * col - 1;
        while(l <= r){
            int mid = l + (r - l) / 2;
            int x = mid / col;
            int y = mid % col;
            if(matrix[x][y] == target) return true;
            else if(matrix[x][y] > target) r = mid - 1;
            else l = mid + 1;
        }
        return false;
    }