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;
}