leetcode Search a 2D Matrix II

原题链接：https://leetcode.com/problems/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;};