1572. Matrix Diagonal Sum-矩阵对角线元素的和

Given a square matrix mat, return the sum of the matrix diagonals.

Only include the sum of all the elements on the primary diagonal and all the elements on the secondary diagonal that are not part of the primary diagonal.

Example 1:

Input: mat = [[1,2,3],
  [4,5,6],
  [7,8,9]]
Output: 25
Explanation: Diagonals sum: 1 + 5 + 9 + 3 + 7 = 25
Notice that element mat[1][1] = 5 is counted only once.

Example 2:
Input: mat = [[1,1,1,1],
  [1,1,1,1],
  [1,1,1,1],
  [1,1,1,1]]
Output: 8

Example 3:
Input: mat = [[5]]
Output: 5

Constraints:

• n == mat.length == mat[i].length
• 1 <= n <= 100
• 1 <= mat[i][j] <= 100

Solution in python:

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