Search a 2D Matrix

https://leetcode.com/problems/search-a-2d-matrix/
 1 class Solution {
 2 public:
 3     bool searchMatrix(vector<vector<int>>& matrix, int target) {
 4         int m=matrix.size();
 5         int n=matrix.at(0).size();
 6         int resM=0;
 7         int resN=0;
 8         for(int i=0;i<m;i++)
 9         {
10             if(matrix.at(i).at(0)<=target)
11                 resM=i;
12             else
13                 break;
14         }
15         for(int j=0;j<n;j++)
16         {
17             if(matrix.at(resM).at(j)<=target)
18                 resN=j;
19             else
20                 break;
21         }
22         if(matrix.at(resM).at(resN)==target)
23             return true;
24         else
25             return false;
26         
27         
28     }
29 };