{
    protected $_len = 0;
    protected $_g = array();
    protected $_visited = array();
    public function __construct()
    {
        $this->_g = array(array(0, 1, 1, 0, 0, 0), array(1, 0, 0, 1, 0, 0), array(1, 0, 0, 1, 1, 1), array(0, 1, 1, 0, 1, 0), array(0, 0, 1, 1, 0, 1), array(0, 0, 1, 0, 1, 0));
        $this->_len = count($this->_g);
        $this->_initVisited();
    }
    protected function _initVisited()
    {
        for ($i = 0; $i < $this->_len; $i++) {
            $this->_visited[$i] = 0;
        }
    }
    public function depthFirst($vertex)
    {
        $this->_visited[$vertex] = 1;
        echo $vertex . "\n";
        for ($i = 0; $i < $this->_len; $i++) {
            if ($this->_g[$vertex][$i] == 1 && !$this->_visited[$i]) {
                $this->depthFirst($i);
            }
        }
    }
}
$g = new Graph();
// 2 0 1 3 4 5
$g->depthFirst(2);