Copy list with random pointer

 1 /**
 2  * Definition for singly-linked list with a random pointer.
 3  * struct RandomListNode {
 4  *     int label;
 5  *     RandomListNode *next, *random;
 6  *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     RandomListNode *copyRandomList(RandomListNode *head) {
12         
13         if (head == NULL) return NULL;
14         RandomListNode *result = new RandomListNode(head->label), *next, *random;
15         
16         unordered_map<RandomListNode*, RandomListNode*> dict;
17         dict[head] = result;
18         
19         while (head){
20             
21             if (head->random){
22                 
23                 if (dict[head->random]) dict[head]->random = dict[head->random];
24                 else{
25                     dict[head->random] = new RandomListNode(head->random->label);
26                     dict[head]->random = dict[head->random];
27                 }
28             }
29             
30             if (head->next){
31                 
32                 if (dict[head->next]) dict[head]->next = dict[head->next];
33                 else{
34                     dict[head->next] = new RandomListNode(head->next->label);
35                     dict[head]->next = dict[head->next];
36                 }
37             }
38             head = head->next;
39         }
40         return result;
41     }
42 };