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.

从右上角开始，若目标值比该值大，行++，否则列–

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