题目：

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.

思路：

二分查找

package array;public class SearchA2DMatrix {    public boolean searchMatrix(int[][] matrix, int target) {        int m;        int n;        if (matrix == null || (m = matrix.length) == 0 || (n = matrix[0].length) == 0) return false;        int start = 0;        int end = m * n - 1;        while (start <= end) {            int mid = (end - start) / 2 + start;            int i = mid / n;            int j = mid - i * n;            if (matrix[i][j] == target)                return true;            if (matrix[i][j] < target)                start = mid + 1;            else                end = mid - 1;        }                return false;    }    public static void main(String[] args) {        // TODO Auto-generated method stub        int[][] matrix = {                          { 1, 3, 5, 7 },                          { 10, 11, 16, 20 },                          { 23, 30, 34, 50}                        };        SearchA2DMatrix s = new SearchA2DMatrix();        System.out.println(s.searchMatrix(matrix, 8));    }}