PHP获取二叉树镜像的方法

<?php
/*class TreeNode{
 var $val;
 var $left = NULL;
 var $right = NULL;
 function __construct($val){
  $this->val = $val;
 }
}*/
function Mirror(&$root)
{
 if($root == NULL)
  return 0;
 $queue = array();
 array_push($queue, $root);
 while(!empty($queue)){
  $node = array_shift($queue);
  $tmp = $node->left;
  $node->left = $node->right;
  $node->right = $tmp;
  if($node->left != NULL)
   array_push($queue, $node->left);
  if($node->right != NULL)
   array_push($queue, $node->right);
 }
}