本次选择的题目是

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.

Solution:
可以从四个角任意选一个开始，每次比较都靠近得数。

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