PHP实现合并两个排序链表的方法

<?php
/*class listnode{
 var $val;
 var $next = null;
 function __construct($x){
  $this->val = $x;
 }
}*/
function merge($phead1, $phead2)
{
 if($phead1 == null)
  return $phead2;
 if($phead2 == null)
  return $phead1;
 $rehead = new listnode();
 if($phead1->val < $phead2->val){
  $rehead = $phead1;
  $phead1 = $phead1->next;
 }else{
  $rehead = $phead2;
  $phead2 = $phead2->next;
 }
 $p = $rehead;
 while($phead1&&$phead2){
  if($phead1->val <= $phead2->val){
   $p->next = $phead1;
   $phead1 = $phead1->next;
   $p = $p->next;
  }
  else{
   $p->next = $phead2;
   $phead2 = $phead2->next;
   $p = $p->next;
  }
 }
 if($phead1 != null){
  $p->next = $phead1;
 }
 if($phead2 != null)
  $p->next = $phead2;
 return $rehead;
}