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.

for every element, represented by M[i][j], the average of M[i][j] and its neighbors should be the sum of (itself and its **valid** neighbors' value) divided by **valid** count

for every M[i][j], there are 8 neighbors, some of them may be index out of boundary, If it's neighbor's index is valid, then add it to sum, and count++

code below

```
class Solution {
public int[][] imageSmoother(int[][] M) {
if(M==null||M.length==0) return new int[][];
int n=M.length;
int m=M[0].length;
int res[][]=new int[n][m];
for(int i=0;i<n;i++){
for(int j=0;j<m;j++){
res[i][j]=avg(M,i,j,n,m);
}
}
return res;
}
public int avg(int[][] M,int x,int y,int n,int m){
int sum=0;
int count=0;
int[] valueAndCount=new int[]{0,0};
for(int[] co:new int[][]{{x,y},{x,y-1},{x,y+1},{x-1,y},{x+1,y},{x+1,y-1},{x+1,y+1},{x-1,y-1},{x-1,y+1}}){
valueAndCount=valueAndCount(M,co[0],co[1],n,m);
sum+=valueAndCount[0];
count+=valueAndCount[1];
}
return sum/count;
}
public int[] valueAndCount(int[][] M,int x,int y,int n,int m){
boolean valid=x>=0&&x<n&&y>=0&&y<m;
return new int[]{valid?M[x][y]:0,valid?1:0};
}
}
```