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 head;
        }
        
        RandomListNode *newHead=NULL,*p=head,*q;
        while(p!=NULL){
            q= new RandomListNode(p->label);
            q->next=p->next;
            p->next=q;
            p=q->next;
        } 
        
        p=head;
        while(p!=NULL){
            q=p->next;
            if(p->random!=NULL){
                q->random = p->random->next;
            } 
            p=q->next;
        }
        
        p=head;
        newHead=head->next;
        q=newHead;
        
        while(p!=NULL){
            p->next=q->next;
            p=p->next;
            if(p!=NULL){
                q->next=p->next;
            }else{
                q->next=NULL;
            }
            q=q->next;
        }
        
        return newHead;
    }
};