Diagonal Difference

Given a square matrix, calculate the absolute difference between the sums of its diagonals.

For example, the square matrix arr is shown below:

1
2
3

1 2 3
4 5 6
9 8 9

The left-to-right diagonal = 1 + 5 + 9 = 15. The right to left diagonal = 3 + 5 + 9 = 17. Their absolute difference is |15 - 17| = 2.

Function Description

Complete the diagonalDifference function in the editor below. It must return an integer representing the absolute diagonal difference.

diagonalDifference takes the following parameter:

• arr: an array of integers .

Input Format

The first line contains a single integer, n, the number of rows and columns in the matrix arr. Each of the next n lines describes a row, arr[i], and consists of n space-separated integers arr[i][j].

Constraints

-100 <= arr[i][j] <= 100

Output Format

Print the absolute difference between the sums of the matrix’s two diagonals as a single integer.

Sample Input

1
2
3
4

3
11 2 4
4 5 6
10 8 -12

Sample Output

1

15

Explanation

The primary diagonal is:

1
2
3

11
   5
     -12

Sum across the primary diagonal: 11 + 5 - 12 = 4

The secondary diagonal is:

1
2
3

     4
   5
10

Sum across the secondary diagonal: 4 + 5 + 10 = 19
Difference: |4 - 19| = 15

Note: |x| is the absolute value of x

Solution

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3
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5
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8
9
10
11
12
13
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15
16
17
18

/*
 * Complete the 'diagonalDifference' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts 2D_INTEGER_ARRAY arr as parameter.
 */

function diagonalDifference(arr) {
    // Write your code here
    let { first, second } = (arr || []).reduce((target, item, index) => {
        target['first'] += arr[index][index];
        target['second'] += arr[index][arr.length - index - 1];

        return target;
    }, { first: 0, second: 0 });

    return Math.abs(first - second);
}