Find the larges difference between indexes of equal array items

index_diff.php

<?php

function solution1($arr) {
    $n = count($arr);

    $diff = $n;

    for ($diff = $n; $diff >= 0; $diff--) {
        for ($i = $n - $diff; $i >= 0; $i--) {
            $j = $diff + $i - 1;

            if ($arr[$i] == $arr[$j]) {
                return $diff - 1;
            }
        }
    }
}

echo solution([1, 3, 8, 4, 2, 1, 4, 9]);