leetcode 661. Image Smoother( Python )

描述

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
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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].
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解析

根據題意，就是把 M 中，每一個位置上的數字變成它周圍數字（包括自身）總和的平均數，若是是角落的或者邊緣的數字，那就只計算若干個數字的平均值，時間複雜度爲 O(N) ，N 爲全部元素的長度，空間複雜度爲 O(N)。

解答

class Solution(object):
def imageSmoother(self, M):
    """
    :type M: List[List[int]]
    :rtype: List[List[int]]
    """
    R,C = len(M),len(M[0])
    result = [[0]*C for _ in range(R)]
    for r in range(R):
        for c in range(C):
            count = 0
            for rr in (r-1,r,r+1):
                for cc in (c-1,c,c+1):
                    if 0<=rr<R and 0<=cc<C:
                        result[r][c] += M[rr][cc]
                        count+=1
            result[r][c]/=count
    return result
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運行結果

Runtime: 648 ms, faster than 58.48% of Python online submissions for Image Smoother.
Memory Usage: 12.1 MB, less than 40.60% of Python online submissions for Image Smoother.
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