leetcode | 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.

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.

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