题目连接

https://leetcode.com/problems/search-a-2d-matrix-ii/

Search a 2D Matrix II

Description

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.

二分。。

class Solution {
public:
	bool searchMatrix(vector<vector<int>>& matrix, int target) {
		if (matrix.empty() || matrix[0].empty()) return false;
		n = matrix.size();
		for (int i = 0; i < n; i++) {
			It p = lower_bound(matrix[i].begin(), matrix[i].end(), target);
			if (p != matrix[i].end() && *p == target) return true;
		}
		return false;
	}
private:
	int n;
	typedef vector<int>::iterator It;
};