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:
void duplicateList(RandomListNode* head)
{
if(head==NULL)return;
RandomListNode* p = head;
while(p)
{
RandomListNode* tmp = new RandomListNode(p->label);
tmp->next = p->next;
p->next = tmp;
p = tmp->next;
}
}
void setRandom(RandomListNode* head)
{
if(head==NULL)return;
RandomListNode* p = head;
RandomListNode* cpy = p->next;
while(p)
{
if(p->random)
cpy->random = p->random->next;
else
cpy->random = NULL;

p = cpy->next;
if(p)
cpy = p->next;
}
}
RandomListNode* separateList(RandomListNode* head)
{
if(head==NULL)return head;
RandomListNode* phead = head->next;
RandomListNode* p = head;
RandomListNode* p1 = phead;
while(p)
{
p->next = p1->next;
p = p->next;
if(p){
p1->next = p->next;
p1 = p1->next;
}
}
return phead;
}
RandomListNode *copyRandomList(RandomListNode *head) {
// Note: The Solution object is instantiated only once.
duplicateList(head);
setRandom(head);
return separateList(head);
}
};