flipping-an-image.py

# Time:  O(n^2)
# Space: O(1)

# Given a binary matrix A, we want to flip the image horizontally,
# then invert it, and return the resulting image.
#
# To flip an image horizontally means that each row of the image is reversed.
# For example, flipping [1, 1, 0] horizontally results in [0, 1, 1].
#
# To invert an image means that each 0 is replaced by 1, and each 1 is
# replaced by 0.
# For example, inverting [0, 1, 1] results in [1, 0, 0].
#
# Example 1:
#
# Input: [[1,1,0],[1,0,1],[0,0,0]]
# Output: [[1,0,0],[0,1,0],[1,1,1]]
# Explanation: First reverse each row: [[0,1,1],[1,0,1],[0,0,0]].
# Then, invert the image: [[1,0,0],[0,1,0],[1,1,1]]
# Example 2:
#
# Input: [[1,1,0,0],[1,0,0,1],[0,1,1,1],[1,0,1,0]]
# Output: [[1,1,0,0],[0,1,1,0],[0,0,0,1],[1,0,1,0]]
# Explanation: First reverse each row:
#              [[0,0,1,1],[1,0,0,1],[1,1,1,0],[0,1,0,1]].
# Then invert the image: [[1,1,0,0],[0,1,1,0],[0,0,0,1],[1,0,1,0]]
#
# Notes:
# 1. 1 <= A.length = A[0].length <= 20
# 2. 0 <= A[i][j] <= 1

try:
    xrange          # Python 2
except NameError:
    xrange = range  # Python 3


class Solution(object):
    def flipAndInvertImage(self, A):
        """
        :type A: List[List[int]]
        :rtype: List[List[int]]
        """
        for row in A:
            for i in xrange((len(row)+1) // 2):
                row[i], row[~i] = row[~i] ^ 1, row[i] ^ 1
        return A