Search a 2D Matrix II

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 in ascending from left to right.
• Integers in each column are sorted in ascending from top to bottom.

Example:

Consider the following matrix:

[
  [1,   4,  7, 11, 15],
  [2,   5,  8, 12, 19],
  [3,   6,  9, 16, 22],
  [10, 13, 14, 17, 24],
  [18, 21, 23, 26, 30]
]

Given target = 5, return true.

Given target = 20, return false.

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int row, col;
        if ( matrix == null || (row=matrix.length) == 0 || (col=matrix[0].length) == 0) return false; 
        int i=0, j=col-1;
        while (i<row && j>=0) {
            if (matrix[i][j] > target) j--;
            else if (matrix[i][j] < target) i++;
            else return true;
        }
        return false;
    }
}