Flipping an Image — LeetCode 832 Python Solution

The problem

Given an n x n binary matrix image, 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.

Example

Input

image = [[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]].

Python solution

class Solution:
    def flipAndInvertImage(self, image: List[List[int]]) -> List[List[int]]:
        n = len(image)
        for row in image:
            i, j = 0, n - 1
            while i < j:
                if row[i] == row[j]:
                    row[i] ^= 1
                    row[j] ^= 1
                i, j = i + 1, j - 1
            if i == j:
                row[i] ^= 1
        return image

Complexity

Pattern: Bit Manipulation

Use XOR, masks and the low-bit trick to replace whole data structures with an integer. LeetCode 832. Flipping an Image is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Bit Manipulation.

The bit manipulation guide has the Python template for the pattern and the 194 LeetCode problems that use it.

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