### 问题描述

https://leetcode.com/problems/search-a-2d-matrix/#/description

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.
For example,

Consider the following matrix:

[
[1,   3,  5,  7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]


Given target = 3, return true.

### 算法

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