public RandomListNode copyRandomList(RandomListNode head) {
  if (head == null) return null;

  Map<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();
  RandomListNode node = head;
  while (node != null) {
    map.put(node, new RandomListNode(node.label));
    node = node.next;
  }
  node = head;
  while (node != null) {
    map.get(node).next = map.get(node.next);
    map.get(node).random = map.get(node.random);
    node = node.next;
  }
  return map.get(head);
}