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.

原题链接：https://oj.leetcode.com/problems/search-a-2d-matrix/

题目：在m * n 的矩阵中查找目标值是否存在。

比較好的办法就是二分查找。即将矩阵总体看成一个数组来处理。

public boolean searchMatrix(int[][] matrix, int target) {		if(matrix == null || matrix.length == 0 || matrix[0].length == 0)			return false;		int m = matrix.length;		int n = matrix[0].length;		int start = 0;		int end = m * n - 1;		while (start <= end) {			int mid = (start + end) / 2;			int x = mid / n;			int y = mid % n;			if (matrix[x][y] == target)				return true;			if (matrix[x][y] < target)				start = mid + 1;			else				end = mid - 1;		}		return false;	}