240. 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.

 1 Solution 1. Binary Search
 2 // The matrix is divided into 3 parts: smaller, bigger and unknown.
 3 public class Solution {
 4     public boolean searchMatrix(int[][] matrix, int target) {
 5         int m = matrix.length;
 6         int n = matrix[0].length;
 7         int i = 0, j = n-1;
 8         while (i<m && j>=0) {
 9             if (target == matrix[i][j]) return true;
10             if (matrix[i][j] > target) {
11                 j--;
12             }else if (matrix[i][j] < target) {
13                 i++;
14             }
15         }
16         
17         return false;
18     }
19 }