Copy List with Random Pointer (LeetCode HashMap)

Question: A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.
Return a deep copy of the list.

Idea: It can be done recursively or iteratively. In recursive algorithm, use a HashMap<original label, new node> to remember the copied nodes.
In iterative algorithm, use a HashMap<original node, new node> to remember the copied nodes. Iterate through the .next pointer while create an unfinished .random node for later update.

Time: O(n) Space: O(n)

Recursive Code:

 public class Solution {  
   public HashMap<Integer,RandomListNode> copied=new HashMap<Integer,RandomListNode>();  
   public RandomListNode copyRandomList(RandomListNode head) {  
     if(head==null)  
     {  
       return null;  
     }  
     if(copied.containsKey(head.label))  
     {  
       return copied.get(head.label);  
     }  
     RandomListNode newNode=new RandomListNode(head.label);  
     copied.put(head.label,newNode);  
     newNode.next=copyRandomList(head.next);  
     newNode.random=copyRandomList(head.random);  
     return newNode;  
   }  
 }  

Iterative Code:

 public class Solution {  
   public RandomListNode copyRandomList(RandomListNode head) {  
     if(head==null)  
     {  
       return null;  
     }  
     HashMap<RandomListNode,RandomListNode> copied=new HashMap<RandomListNode,RandomListNode>();  
     RandomListNode dummy=new RandomListNode(0);  
     RandomListNode pre=dummy;  
     while(head!=null)  
     {  
       RandomListNode newNode;  
       if(copied.containsKey(head))  
       {  
         newNode=copied.get(head);  
       }  
       else  
       {  
         newNode=new RandomListNode(head.label);  
         copied.put(head,newNode);  
       }  
       pre.next=newNode;  
       if(head.random!=null)  
       {  
         if(copied.containsKey(head.random))  
         {  
           newNode.random=copied.get(head.random);  
         }  
         else  
         {  
           newNode.random=new RandomListNode(head.random.label);  
           copied.put(head.random,newNode.random);  
         }  
       }  
       pre=newNode;  
       head=head.next;  
     }  
     return dummy.next;  
   }  
 }