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

class Solution {    public int[][] imageSmoother(int[][] M) {        if (M == null) return null;        int rows = M.length;        if (rows == 0) return new int[0][];        int cols = M[0].length;        int result[][] = new int[rows][cols];        for (int row = 0; row < rows; row++) {            for (int col = 0; col < cols; col++) {                int count = 0;                int sum = 0;                for (int incR : new int[]{-1, 0, 1}) {                    for (int incC : new int[]{-1, 0, 1}) {                        if (isValid(row + incR, col + incC, rows, cols)) {                            count++;                            sum += M[row + incR][col + incC];                        }                    }                }                result[row][col] = sum / count;            }        }        return result;    }    private boolean isValid(int x, int y, int rows, int cols) {        return x >= 0 && x < rows && y >= 0 && y < cols;    }}