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LeetCode solutions

1677. Matrix Diagonal Sum

My accepted Python solution to LeetCode problem 1677, Matrix Diagonal Sum, running in 0ms.

  • Difficulty: Easy
  • Python
  • Runtime 0ms
  • Memory 17.9MB

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 0ms, memory 17.9MB, accepted 2025-12-29.

python
class Solution:
    def diagonalSum(self, mat: List[List[int]]) -> int:
        # Sum primary diagonal (i,i) and secondary diagonal (i, n-1-i)
        # If n is odd, center is counted twice, so subtract once
        # Time: O(n), Space: O(1)
        n = len(mat)
        total = 0
        for i in range(n):
            total += mat[i][i]  # Primary diagonal
            total += mat[i][n - 1 - i]  # Secondary diagonal
        # If n is odd, center was counted twice
        if n % 2 == 1:
            total -= mat[n // 2][n // 2]
        return total

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