CopyList with Random Pointer -- Leetcode

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.

Answer:
/**
 * 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 null;
       
       
        HashMap<RandomListNode,RandomListNode> hmap = new HashMap<RandomListNode, RandomListNode>();
        RandomListNode newListHead = new RandomListNode(head.label);
        hmap.put(head, newListHead);
       
        RandomListNode prevNew = newListHead, curOld = head.next, curNew=null;
       
        while(curOld!= null){                                                       //copy label and next
            curNew = new RandomListNode(curOld.label);
            hmap.put(curOld,curNew);
            prevNew.next = curNew;
            prevNew = curNew;
            curOld = curOld.next;
        }
        prevNew.next = null;
       
        curOld = head; curNew = newListHead;
        while(curOld!= null){                                                       //copy random
            curNew.random = hmap.get(curOld.random);
            curOld = curOld.next;
            curNew = curNew.next;
        }
       
        return newListHead;
    }
}