LeetCode OJ：Copy List with Random Pointer（复制存在随机链接的链表）

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.

这题用map做其实比较简单，但是一开始没想明白越想越乱，最后看了下别人的实现，思路还是很清晰的，代码如下所示：

 /**
  * Definition for singly-linked list with a random pointer.
  * struct RandomListNode {
  *     int label;
  *     RandomListNode *next, *random;
  *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
  * };
  */

 class Solution {
 public:
     RandomListNode *copyRandomList(RandomListNode *head) {
         unordered_map<RandomListNode *, RandomListNode *> m;
         RandomListNode helper1(), * p1 = &helper1, helper2(), *p2 = &helper2;
         p1->next = head;
         while(p1->next){
             p1 = p1->next;
             RandomListNode * tmpNode = new RandomListNode(p1->label);
             m[p1] = tmpNode;
             p2 = p2->next = tmpNode;
         }
         p1 = &helper1;
         while(p1->next){
             p1 = p1->next;
             if(p1->random){
                 m[p1]->random = m[p1->random];
             }
         }
         return helper2.next;
     }
 };