Copy List with Random Pointer

Description:

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.

Challenge

Could you solve it with O(1) space?

Solution:

/**
* 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:
/
* @param head: The head of linked list with a random pointer.
* @return: A new head of a deep copy of the list.
*/
RandomListNode *copyRandomList(RandomListNode *head) {
if (!head) return nullptr;
auto node = head;
while (node) {
auto tmp = node->next;
node->next = new RandomListNode(node->label);
node->next->next = tmp;
node = tmp;
}
node = head;
while (node) {
if (node->random) node->next->random = node->random->next;
node = node->next->next;
}
node = head;
auto rc = head->next;
while (node) {
auto tmp = node->next->next;
if (tmp) node->next->next = tmp->next;
node->next = tmp;
node = tmp;
}
return rc;
}
};