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1147. Flip Columns For Maximum Number of Equal Rows

My accepted Python solution to LeetCode problem 1147, Flip Columns For Maximum Number of Equal Rows, running in 38ms.

  • Difficulty: Medium
  • Python
  • Runtime 38ms
  • Memory 20.3MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

Python

Accepted on LeetCode — runtime 38ms, memory 20.3MB, accepted 2025-12-29.

python
class Solution:
    def maxEqualRowsAfterFlips(self, matrix: List[List[int]]) -> int:
        # Two rows can be made equal if one is the complement of the other or same
        # Use pattern matching - normalize each row to start with 0
        # Time: O(m*n), Space: O(m*n)
        from collections import Counter
        
        patterns = Counter()
        
        for row in matrix:
            # Normalize: if row[0] is 1, flip all bits
            if row[0] == 1:
                pattern = tuple(1 - x for x in row)
            else:
                pattern = tuple(row)
            patterns[pattern] += 1
        
        return max(patterns.values())

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