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.

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if(matrix.length == 0 || matrix[0].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;
            if(matrix[i][j] < target) i++;
            else j--;
        }
        return false;
    }
}

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。

 参考代码：http://www.cnblogs.com/Dylan-Java-NYC/p/4881258.html