PHP实现按之字形顺序打印二叉树的方法

<?php/*class TreeNode{  var $val;  var $left = NULL;  var $right = NULL;  function __construct($val){    $this->val = $val;  }}*/function MyPrint($pRoot){  if($pRoot == NULL)    return [];  $current = 0;  $next  = 1;  $stack[0] = array();  $stack[1] = array();  $resultQueue = array();  array_push($stack[0], $pRoot);  $i = 0;  $result = array();  $result[0]= array();  while(!empty($stack[0]) || !empty($stack[1])){    $node = array_pop($stack[$current]);    array_push($result[$i], $node->val);    //var_dump($resultQueue);echo "</br>";    if($current == 0){      if($node->left != NULL)        array_push($stack[$next], $node->left);      if($node->right != NULL)        array_push($stack[$next], $node->right);    }else{      if($node->right != NULL)        array_push($stack[$next], $node->right);      if($node->left != NULL)        array_push($stack[$next], $node->left);    }    if(empty($stack[$current])){      $current = 1-$current;      $next  = 1-$next;      if(!empty($stack[0]) || !empty($stack[1])){        $i++;        $result[$i] = array();      }    }  }  return $result;}