#YYPHP で出されたクイズの回答

yyphp_quiz.php

<?php
    $a = [1, [2, [3, [4, [5]]]]];
    $b = [1, 2, 3, 4, 5];

    function f($a) {
        global $ret;
        foreach ($a as $val) {
            if (!is_array($val)) {
                $ret[] = $val;
            } else {
                f($val);
            }
        }
        return $ret;
    }

    $c = f($a);

    if ($b === $c) {
        echo "OK";
    } else {
        echo "NG";
    }