LeetCode 661 : Image Smoother（python）

来源：互联网发布：淘宝新上的宝贝找不到编辑：程序博客网时间：2024/06/07 20:18

好久没更新博客了，最近沉迷于Android和深度学习的研究，python、c++、java等语言都会接触，难免会把一些语法层面的东西记混了。也很久没上Leetcode，感觉现在脑子不够用，只够刷Easy的题。周末闲来无聊逛了一下，看到一道平滑滤波的题。没想到Leetcode也这么与时俱进，竟然出现了图像处理的相关题目。不过由于对python列表复制的不熟，还是成功跳进了一个坑。仅以此文做一些总结。

原题：
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:
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].

解题过程：
一开始一上来觉得很简单，先写个滤波器，然后从左至右，从上至下移动，有一点3*3卷积的feel。当然这中间要判断滤波器覆盖的点是否合法，于是又写了个判断点是否合法的函数。当然，这样的思路是木有问题的。先贴上代码：

class Solution:    def isLegal(self,x,y,i,j):        return (True if((i<x)and(j<y)and(i>=0)and(j>=0)) else False)    def imageSmoother(self, M):        """        :type M: List[List[int]]        :rtype: List[List[int]]        """        x=len(M)        y=len(M[0])        returnM=M        Filter=[[-1,-1],[-1,0],[-1,1],[0,-1],[0,0],[0,1],[1,-1],[1,0],[1,1]]        for i in range(x):            for j in range(y):                legalPointNum=0                graySum=0                for fi in range(9):                        tmpi=i+Filter[fi][0]                        tmpj=j+Filter[fi][1]                        if(self.isLegal(x,y,tmpi,tmpj)):                            graySum+=M[tmpi][tmpj]                            legalPointNum+=1                returnM[i][j]=int(graySum/legalPointNum)        return returnM

结果，一提交，在第12个样例就卡住了：

Your input[[2,3,4],[5,6,7],[8,9,10],[11,12,13],[14,15,16]]Your answer[[4,4,5],[6,6,6],[8,9,9],[11,11,12],[12,12,12]]Expected answer[[4,4,5],[5,6,6],[8,9,9],[11,12,12],[13,13,14]]

来来回回检查了好几遍代码，发现看不出有什么问题，结果就各种print，如下：

class Solution:    def isLegal(self,x,y,i,j):        return (True if((i<x)and(j<y)and(i>=0)and(j>=0)) else False)    def imageSmoother(self, M):        """        :type M: List[List[int]]        :rtype: List[List[int]]        """        x=len(M)        y=len(M[0])        returnM=M        Filter=[[-1,-1],[-1,0],[-1,1],[0,-1],[0,0],[0,1],[1,-1],[1,0],[1,1]]        for i in range(x):            for j in range(y):                legalPointNum=0                graySum=0                for fi in range(9):                        tmpi=i+Filter[fi][0]                        tmpj=j+Filter[fi][1]                        if(self.isLegal(x,y,tmpi,tmpj)):                            print(tmpi)                            print(tmpj)                            graySum+=M[tmpi][tmpj]                            legalPointNum+=1                print(graySum)                print(legalPointNum)                returnM[i][j]=int(graySum/legalPointNum)        return returnM

果然发现当i=0，j=1的时候就错了，结果来来回回检查代码，感觉returnM=M 有问题，于是考虑到肯定是list复制的问题了，目测这么写returnM和M的地址是一样的，结果print了一下id，果然是一样：

print(id(returnM))print(id(M))

结果老老实实跑去google，发现了这篇博文的总结：
http://www.cnblogs.com/ifantastic/p/3811145.html
原来如此！
改过来之后就AC了：

class Solution:    def isLegal(self,x,y,i,j):        return (True if((i<x)and(j<y)and(i>=0)and(j>=0)) else False)    def imageSmoother(self, M):        """        :type M: List[List[int]]        :rtype: List[List[int]]        """        x=len(M)        y=len(M[0])        returnM=copy.deepcopy(M)        # returnM=M        Filter=[[-1,-1],[-1,0],[-1,1],[0,-1],[0,0],[0,1],[1,-1],[1,0],[1,1]]        for i in range(x):            for j in range(y):                legalPointNum=0                graySum=0                for fi in range(9):                        tmpi=i+Filter[fi][0]                        tmpj=j+Filter[fi][1]                        if(self.isLegal(x,y,tmpi,tmpj)):                            # print(tmpi)                            # print(tmpj)                            graySum+=M[tmpi][tmpj]                            legalPointNum+=1                # print(graySum)                # print(legalPointNum)                returnM[i][j]=int(graySum/legalPointNum)        return returnM#没过的样例#[[2,3,4],[5,6,7],[8,9,10],[11,12,13],[14,15,16]]

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