661. Image Smoother

Given a 2D integer matrix M representing the gray scale of an image, you need to design a smoother to make the gray scale of each cell becomes the average gray scale (rounding down) of all the 8 surrounding cells and itself. If a cell has less than 8 surrounding cells, then use as many as you can.

Example 1:

Input:
[[1,1,1],
 [1,0,1],
 [1,1,1]]
Output:
[[0, 0, 0],
 [0, 0, 0],
 [0, 0, 0]]
Explanation:
For the point (0,0), (0,2), (2,0), (2,2): floor(3/4) = floor(0.75) = 0
For the point (0,1), (1,0), (1,2), (2,1): floor(5/6) = floor(0.83333333) = 0
For the point (1,1): floor(8/9) = floor(0.88888889) = 0

C++(173ms):

class Solution {
public:
    vector<vector<int>> imageSmoother(vector<vector<int>>& M) {
        int n = M.size() ; 
        int m = M[0].size();
        if (n == 0 || m == 0)
            return vector<vector<int>>() ;
        vector<vector<int>> dirs = {{0,1},{0,-1},{1,0},{-1,0},{-1,-1},{1,1},{-1,1},{1,-1}};
        vector<vector<int>> res(n) ;
        for(int i = 0 ; i < n ; i++){
            for (int j = 0 ; j < m ; j++){
                res[i].resize(m) ;
                int sum = M[i][j] ;
                int cnt = 1 ;
                for(int k = 0 ; k < 8 ; k++){
                    int x = i + dirs[k][0] ;
                    int y = j + dirs[k][1] ;
                    if (x < 0 || x > n-1 || y < 0 || y > m-1)
                        continue ;
                    sum += M[x][y] ;
                    cnt++ ;
                }
                res[i][j] = sum/cnt ;
            }
        }
        return res ;
    }
};

 或者   vector<vector<int>> res(n , vector<int>(m,0)) ;