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.

从左上角开始，大于target向前，小于向下。

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