Diagonal difference of 2D array - PHP. Given a square matrix, calculate the absolute difference between the sums of its diagonals... Note: |x| is the absolute value of x

diagonal-difference.php

// Complete the diagonalDifference function below.
function diagonalDifference($arr) {
    $d_ar = [];
    $main_len = count($arr);

    foreach($arr as $key => $ar) {
    	$sub_len = count($ar);
		if($main_len != $sub_len) {
			throw new Exception('Array index count mismatched. Hence this is not square array.');
		}
        $d_ar[0][] = $ar[$key];
        $d_ar[1][] = $ar[($main_len-$key-1)];
    }
    return abs((array_sum($d_ar[0]) - array_sum($d_ar[1])));
}

$arr = [
    [1,2,3],
    [4,5,6],
    [9,8,9]
];

$result = diagonalDifference($arr);
echo $result