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) = 0For the point (0,1), (1,0), (1,2), (2,1): floor(5/6) = floor(0.83333333) = 0For the point (1,1): floor(8/9) = floor(0.88888889) = 0

Note:

1. The value in the given matrix is in the range of [0, 255].
2. The length and width of the given matrix are in the range of [1, 150].

将图像平滑处理，即每个像素取以其为中心的九个格的平均值。注意一下边界的情况即可。

代码：

class Solution {public:    vector<vector<int>> imageSmoother(vector<vector<int>>& M) {        vector<vector<int>> res(M);        for(int i = 0; i < M.size(); ++i) {            for(int j = 0; j < M[0].size(); ++j) {                res[i][j] = avg(M, i, j);            }        }        return res;    }private:    int avg(vector<vector<int>>& M, int r, int c) {        int cnt = 0, sum = 0;        for(int i = r - 1; i <= r + 1; ++i) {            for(int j = c - 1; j <= c + 1; ++j) {                if(i < 0 || i >= M.size()) continue;                if(j < 0 || j >= M[0].size()) continue;                cnt++;                sum += M[i][j];            }        }        return sum / cnt;    }};