听了波波老师的课爱上递归了！使用起来有种四两拨千斤的快感。但是个问题请教，与普通的循环遍历比，它的性能是否更好呢？
贴一下自己用PHP写的二叉树，学习这门课的PHPer一起加油吧！

<?php
class Node{
	public $value,$left,$right;
	public function __construct($value,Node $left = null,Node $right = null){
		$this->value = $value;
		$this->left = $left;
		$this->right = $right;
	}
}
class BST{
	private $root,$size;
    public function	__construct(){
    	$this->root = null;
    	$this->size = 0;
	}
	public function add($e){
		$this->root = $this->_add($this->root,$e);
	}
	private function _add($root,$e){
		if($root == null){
			$this->size++;
			return new Node($e);
		}
		if($e > $root->value )
			$root->right = $this->_add($root->right,$e);
		else if($e < $root->value)
			$root->left = $this->_add($root->left,$e);
		return $root;
	}
	public function contains($value){
		if($this->root->value == $value)
			return $this->root;
		else if ($this->root->value > $value)
			return $this->_contains($value,$this->root->right);
		else if ($this->root->value < $value)
			return $this->_contains($value,$this->root->left);
	}
	private function _contains($value,$root){
		if($root == null)
			return false;
		if($root->value == $value)
			return true;
		else if ($root->value > $value)
			return $this->_contains($value,$root->right);
		else if($root->value < $value)
			return $this->_contains($value,$root->left);
	}
}
$bst = new BST();
$bst->add(21);
$bst->add(23);
$bst->add(56);
$bst->add(24);
$bst->add(45);
var_dump($bst->contains(23));
var_dump($bst->contains(34));