reverse_linked_list.php

<?php
class Node
{
    /**
     * @var string
     */
    private $value;

    /**
     * @var Node
     */
    private $next;

    /**
     * Node constructor.
     * @param string $value
     * @param Node $next
     */
    public function __construct(string $value, Node $next = null)
    {
        $this->value = $value;
        $this->setNext($next);
    }

    static public function fromString(string $s)
    {
        $head = $last = null;
        foreach (str_split($s) as $char) {
            $node = new Node($char);
            if ($last instanceof Node) {
                $last->setNext($node);
                $last = $node;
            } else {
                $head = $last = $node;
            }
        }
        return $head;
    }

    static public function toString(Node $node = null)
    {
        $s = '';
        while ($node instanceof Node) {
            $s .= $node;
            $node = $node->getNext();
        }
        return $s;
    }

    static public function reverse(Node $node)
    {
        $prev = null;
        while ($node instanceof Node) {
            $next = $node->getNext();
            $node->setNext($prev);
            list($prev, $node) = [$node, $next];
        }
        return $prev;
    }

    /**
     * @return Node|null
     */
    public function getNext()
    {
        return $this->next;
    }

    /**
     * @param Node $next
     */
    public function setNext(Node $next = null)
    {
        $this->next = $next;
    }

    public function __toString()
    {
        return $this->value;
    }
}

$test = [
    '',
    'h',
    'hello'
];

foreach ($test as $s) {
    $passed = strrev($s) === Node::toString(Node::reverse(Node::fromString($s)));
    printf("'%s': %s\n", $s, $passed ? 'PASS' : 'FAIL');
}