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) 

    {

        //insert copy

        if(head==NULL) return NULL;

        RandomListNode* p=head;

        while(p!=NULL)

        {

            RandomListNode* pnext=p->next;

            RandomListNode* pnew=new RandomListNode(p->label);

            p->next=pnew;

            pnew->next=pnext;

            p=pnext;

        }

        //the pointer

        RandomListNode* p1=head;

        RandomListNode* p2=head->next;

        while(true)

        {

            if(p1->random!=NULL) p2->random=p1->random->next;

            p1=p1->next->next;

            if(p1==NULL) break;

            p2=p2->next->next;

        }

        //split the 2 list

        RandomListNode* phead=head->next;

        p1=head;

        p2=phead;

        while(true)

        {

            RandomListNode* p1next=p1->next->next;

            p1->next=p1next;

            if(p1next==NULL) break;

            p2->next=p1next->next;

            

            p1=p1next;

            p2=p1next->next;

        }

        return phead;

    }

};