Copy List with Random Pointer (leetcode)

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) {
return NULL;
}
// modify this list
// for exaple if the original list is  1->2->3->4->5->6
// then the modified list will be 1->1->2->2->3->3->4->4->5->5->6->6
RandomListNode * curr = head;
while (curr) {
RandomListNode * new_node = new RandomListNode(curr->label);
new_node->next = curr->next;
curr->next = new_node;
curr = new_node->next;
}
//set the random pointer of the new added node points to the right place
curr = head;
while (curr) {
RandomListNode *post = curr->next;
if (curr->random) {
post->random = curr->random->next;
}
curr = post->next;
}
//split the list into two lists
//and new_head points to the new list
//head points to the original list
RandomListNode * new_head = NULL;
RandomListNode * new_curr = NULL;
curr = head;
while (curr) {
if (!new_head) {
new_head = new_curr = curr->next;
} else {
new_curr = curr->next;
}
curr->next = new_curr->next;
curr = curr->next;
if (curr) {
new_curr->next = curr->next;
}
}
return new_head;
}
};