[leetcode] Search a 2D Matrix

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：逐行搜索，其实可以对行和列分别用二分搜索，参考，http://www.cnblogs.com/remlostime/archive/2012/11/14/2770127.html

代码：

class Solution {public:    bool searchMatrix(vector<vector<int> > &matrix, int target) {        int i = 0, j = matrix[0].size() - 1;         while (i < matrix.size() && j >= 0)         {             if (target == matrix[i][j])                 return true;             else if (target < matrix[i][j])                 j--;             else                 i++;         }         return false;    }};