[LeetCode]Copy List with Random Pointer

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.

/** * 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) {        if(head==NULL)            return NULL;        map<RandomListNode*,RandomListNode*> m;        RandomListNode* prehead = head;        RandomListNode* ret = new RandomListNode(head->label);        RandomListNode* pret = ret;        while(head!=NULL){            m[head] = ret;            if(head->next!=NULL)            ret->next = new RandomListNode(head->next->label);            ret = ret->next;            head = head->next;        }        while(prehead!=NULL){            if(prehead->random==NULL){                (m[prehead])->random==NULL;            }            else (m[prehead])->random = m[prehead->random];            prehead = prehead->next;        }        return pret;    }};