Search a 2D Matrix II

Problem:

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.

For 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.

Analysis:

The bottom-left and top-right numbers are special. Take bottom-left as an example, any number less than 18, go up, greater than 18 go right. 

Solution:

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