240. Search a 2D Matrix II java solutions

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 public class Solution {
 2     public boolean searchMatrix(int[][] matrix, int target) {
 3         if(matrix.length == 0 || matrix[0].length == 0) return false;
 4         int i = 0,j = matrix[0].length-1;
 5         while(i < matrix.length && j >= 0){
 6             if(matrix[i][j] == target) return true;
 7             if(matrix[i][j] < target) i++;
 8             else j--;
 9         }
10         return false;
11     }
12 }

该题矩阵比较特殊，可以从右上角X开始比较， 如果target > X,则到下一行，如果target < X,则要往回走一列。题目在编程之美里面出现过。

解法2： 该题也可以使用二分法进行查找。