Leetcode 1572. Matrix Diagonal Sum

Posted 2021-08-26 SnailTyan

文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. Description

2. Solution

**解析：**Version 1，简单根据主对角线和次对角线的位置规律，把对应位置的数加起来即可，如果是奇数行，要考虑中心元素被加了两次，因此要减掉重复相加。

• Version 1

class Solution:
    def diagonalSum(self, mat: List[List[int]]) -> int:
        n = len(mat)
        result = 0
        for i in range(n):
            result += mat[i][i]
            result += mat[n-i-1][i]
        if n % 2 == 1:
            mid = n // 2
            result -= mat[mid][mid]
        return result

Reference

1. https://leetcode.com/problems/matrix-diagonal-sum/