HackerRank: Diagonal Difference Solution using PHP (Algorithm)

Diagonal Difference Solution

Given a square matrix, calculate the absolute difference between the sums of its diagonals.
For example, the square matrix is shown below:

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.

Difference 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

11 2 4
4 5 6
10 8 -12

Sample Output

15

Explanation
The primary diagonal is:

11
5
-12

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

The secondary diagonal is:

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 (Base on how i solved it)

$first = 0;
$second = 0;
$n = sizeof($arr);
for ($i = 0; $i < $n; $i++){
for ($j = 0; $j < $n; $j++){
    if ($i === $j){
        $first += $arr[$i][$j];
    }
        if ($i + $j === $n - 1){
            $second += $arr[$i][$j];
        }
    }
}
return abs($first - $second);
}