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(0), * p1 = &helper1, helper2(0), *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;
    }
};