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.

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/**

 * 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:

    void copyFirst(RandomListNode *head){

        

        RandomListNode *pcur, *pnext, *q;

        pcur = head;

        while(pcur != NULL){

            pnext = pcur->next;

            q = new  RandomListNode(pcur->label);

            q->next = pnext;

            pcur->next = q;

            pcur = pnext;

        }

    }

    void fixRandom(RandomListNode * head){

        

        RandomListNode *ph = head;

        while(ph!=NULL){

            if(ph->random != NULL)

                ph->next->random = ph->random->next;

            ph = ph->next->next;    

        }

    }

    RandomListNode * getCopy(RandomListNode *head){

            

        RandomListNode *p,*rcur,*q, *res;

        res = NULL; p = head;rcur = NULL;

        while(p != NULL){

            q  = p->next;

            p->next = q->next;

            p = p->next;

            if(res == NULL){

                res = q;

                rcur = q;

            }else{

                rcur->next = q;

                rcur = q;

            }

        }

       // rcur->next = NULL;

        return res;

        

    }

    RandomListNode *copyRandomList(RandomListNode *head) {

        // Note: The Solution object is instantiated only once and is reused by each test case.

        if(head == NULL) return NULL;

        copyFirst(head);

        fixRandom(head);

        return getCopy(head);

        

    }

};