copy list with random pointer using HashMap

CopyListwithRandomPonterHashMap.java

/**
 * Definition for singly-linked list with a random pointer.
 * class RandomListNode {
 *     int label;
 *     RandomListNode next, random;
 *     RandomListNode(int x) { this.label = x; }
 * };
 */
public class Solution {
    public RandomListNode copyRandomList(RandomListNode head) {
        if(head == null)
            return head;
        
        HashMap<RandomListNode, RandomListNode> hm = new HashMap<RandomListNode, RandomListNode>();
        RandomListNode current = head;
        while(current != null){
            hm.put(current, new RandomListNode(current.label));
            current = current.next;
        }
        
        current = head;
        while(current != null){
            hm.get(current).next = hm.get(current.next);
            hm.get(current).random = hm.get(current.random);
            current = current.next;
        }
        
        return hm.get(head);
    }
}