main-diagonal-sum.md

Main Diagonal Sum

Problem Description

You are given a N X N integer matrix. You have to find the sum of all the main diagonal elements of A. Main diagonal of a matrix A is a collection of elements A[i, j] such that i = j.

Problem Constraints

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

Input Format

There are 1 lines in the input. First 2 integers R, C are the number of rows and columns. Then R * C integers follow corresponding to the rowwise numbers in the 2D array A.

Output Format

Return an integer denoting the sum of main diagonal elements.

Example Input

Input 1:
3 3 1 -2 -3 -4 5 -6 -7 -8 9

Input 2:
2 2 3 2 2 3

Example Output

Output 1:
15

Output 2:
6

Example Explanation

Explanation 1:
The size of matrix is 3.
So, considering the indexing from 0.
Main diagonal elements will be A[0][0], A[1][1] and A[2][2]
A[1][1] + A[2][2] + A[3][3] = 1 + 5 + 9 = 15

Explanation 2:
The size of matrix is 2.
So, considering the indexing from 0.
Main diagonal elements will be A[0][0] and A[1][1].
A[1][1] + A[2][2] = 3 + 3 = 6

Output

function mainDiagonalSum(A){
        let sum = 0;
        for(let i = 0 ; i < A.length ; i++){
            sum = Number(sum) + Number(A[i][i])
        }
        return sum
}