# Search a 2D Matrix II

### 描述​

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.

### 代码​

// Search a 2D Matrix II// 时间复杂度O(m + n)，空间复杂度O(1)public class Solution {    public boolean searchMatrix(int[][] matrix, int target) {        if(matrix.length==0 || matrix[0].length==0) return false;        int i = 0;        int j = matrix[0].length-1;        while(i < matrix.length && j >= 0) {            final int x = matrix[i][j];            if(target == x) {                return true;            } else if (x < target) {                ++i;            } else {                --j;            }        }        return false;    }}