leetCode---Search a 2D Matrix II

一. 题目：Search a 2D Matrix II

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. 思路分析

题目大意：给定一个二位矩阵，矩阵从左到右，从上到下是递增的，给定一个目标值，看能否从举证中找到。思路分析：结合

矩阵的特点，矩阵是从左到右，从上到下是递增的，那我们可以选择初始寻找点最左下方的值，如果比目标值大，向右搜索，比目标值小，

向上搜索，直到找到目标值，没有则返回fasle；代码如下：

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