Copy List with Random Pointer

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.

/**
 * 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) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if (head == null){
            return null;
        }
        RandomListNode result = new RandomListNode(head.label);
        RandomListNode p = head.next;
        RandomListNode pc = result;
        HashMap ht = new HashMap();
        ht.put(head,result);
        while (p!=null) {
            RandomListNode tmp = new RandomListNode(p.label);
            pc.next = tmp;
            ht.put(p,tmp);
            p = p.next;
            pc = pc.next;
        }
        p = head;
        pc = result;
        while (p!=null){
            if (p.random!=null){
                pc.random = (RandomListNode) ht.get(p.random);
            }
            p = p.next;
            pc = pc.next;
        }
        return result;
    }
}