138. Copy List with Random Pointer

 1 RandomListNode *copyRandomList(RandomListNode *head) 
 2     {
 3         unordered_map<RandomListNode *, RandomListNode *> listMap;
 4         RandomListNode *dummy = new RandomListNode(0), *oldNode, *newNode, *r;
 5         
 6         r = dummy;
 7         for (oldNode = head; oldNode != NULL; oldNode = oldNode->next)
 8         {
 9             newNode = new RandomListNode(oldNode->label);
10             listMap[oldNode] = newNode;
11             r->next = newNode;
12             r = newNode;
13         }
14         
15         for (oldNode = head; oldNode != NULL; oldNode = oldNode->next)
16             listMap[oldNode]->random = listMap[oldNode->random];
17         
18         r = dummy->next;
19         delete dummy;
20         return r;
21     }