[leetcode]Copy List with Random Pointer

/**
 * 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) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        RandomListNode *p = head;
        while (p != NULL) {
            RandomListNode *t = new RandomListNode(p->label);
            t->next = p->next;
            p->next = t;
            p = t->next;
        }
        p = head;
        while (p != NULL) {
            if (p->random != NULL) 
                p->next->random = p->random->next;
            else
                p->next->random = NULL;
            p = p->next->next;
        }
        RandomListNode *new_head, *new_tail;
        new_head = new_tail = NULL;
        p = head;
        while (p != NULL) {
            if (new_head == NULL) {
                new_head = new_tail = p->next;
            } else {
                new_tail->next = p->next;
                new_tail = p->next;
            }
            p->next = p->next->next;
            p = p->next;
        }
        if (new_tail != NULL) 
            new_tail->next = NULL;
        return new_head;
    }
};