## 题目描述：

LeetCode 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
```

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].

## Python代码：

``````class Solution(object):
def imageSmoother(self, M):
"""
:type M: List[List[int]]
:rtype: List[List[int]]
"""
dx, dy = [-1, 0, 1], [-1, 0, 1]
w, h = len(M), len(M)
N = []
for x in range(w):
row = []
for y in range(h):
nbs = [M[x + i][y + j] for i in dx for j in dy \
if 0 <= x + i < w and 0 <= y + j < h]
row.append(sum(nbs) / len(nbs))
N.append(row)
return N
``````

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