DFS Algorithm in PHP

gistfile1.php

<?php

class Node
{
    public $name;
    public $linked = array();

    public function __construct($name)
    {
        $this->name = $name;
    }

    public function link_to(Node $node, $also = true)
    {
        if (!$this->linked($node)) $this->linked[] = $node;
        if ($also) $node->link_to($this, false);
        return $this;
    }

    private function linked(Node $node)
    {
        foreach ($this->linked as $l) { if ($l->name === $node->name) return true; }
        return false;
    }

    public function not_visited_nodes($visited_names)
    {
        $ret = array();
        foreach ($this->linked as $l) {
            if (!in_array($l->name, $visited_names)) $ret[] = $l;
        }
        return $ret;
    }
}

/* Building Graph */
$root = new Node('root');
foreach (range(1, 6) as $v) {
        $name = "node{$v}";
        $$name = new Node($name);
}
$root->link_to($node1)->link_to($node2);
$node1->link_to($node3)->link_to($node4);
$node2->link_to($node5)->link_to($node6);
$node4->link_to($node5);


/* Searching Path */
function dfs(Node $node, $path = '', $visited = array())
{
    $visited[] = $node->name;
    $not_visited = $node->not_visited_nodes($visited);
    if (empty($not_visited)) {
        echo 'path : ' . $path . '->' . $node->name . PHP_EOL;
        return;
    }
    foreach ($not_visited as $n) dfs($n, $path . '->' . $node->name, $visited);
}

dfs($root);
// path : ->root->node1->node3
// path : ->root->node1->node4->node5->node2->node6
// path : ->root->node2->node5->node4->node1->node3
// path : ->root->node2->node6