image-smoother.py

# Time:  O(m * n)
# Space: O(1)

# 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].

class Solution(object):
    def imageSmoother(self, M):
        """
        :type M: List[List[int]]
        :rtype: List[List[int]]
        """
        def getGray(M, i, j):
            directions = [[-1, -1], [0, -1], [1, -1], \
                          [-1,  0], [0,  0], [1,  0], \
                          [-1,  1], [0,  1], [1,  1]]
        
            total, count = 0, 0.0
            for direction in directions:
                ii, jj = i + direction[0], j + direction[1]
                if 0 <= ii < len(M) and 0 <= jj < len(M[0]):
                    total += M[ii][jj]
                    count += 1.0
            return int(total / count)

        result = [[0 for _ in xrange(len(M[0]))] for _ in xrange(len(M))]
        for i in xrange(len(M)):
            for j in xrange(len(M[0])):
                result[i][j] = getGray(M, i, j);
        return result