1572. Matrix Diagonal Sum

Difficulty: Easy

Related Topics: Array

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

Language: Python3

class Solution:
    def diagonalSum(self, mat: List[List[int]]) -> int:
        rep=0
        r,c=0,0
        while r<len(mat) and c<len(mat[0]):
            rep+=mat[r][c]
            r+=1
            c+=1
        r,c=0,len(mat[0])-1
        while r<len(mat) and c>=0:
            rep+=mat[r][c]
            r+=1
            c-=1
        if len(mat)%2!=0:
            rep-=mat[len(mat)//2][len(mat)//2]
        return rep