Minor Diagonal Sum

Problem Description

You are given a N X N integer matrix. You have to find the sum of all the minor diagonal elements of A.

Minor diagonal of a M X M matrix A is a collection of elements A[i, j] such that i + j = M + 1 (where i, j are 1-based).

1 <= N <= 10^3
-1000 <= A[i][j] <= 1000

First and only argument is a 2D integer matrix A.

Return an integer denoting the sum of minor diagonal elements.

Input 1:
 A = [[1, -2, -3],
      [-4, 5, -6],
      [-7, -8, 9]]

Input 2:
A = [[3, 2],
      [2, 3]]

Output 1:
-5

Output 2:
4

Explanation 1:
A[1][3] + A[2][2] + A[3][1] = (-3) + 5 + (-7) = -5

Explanation 2:
A[1][2] + A[2][1] = 2 + 2 = 4

Java

Python

JavaScript