/**
 * Definition for singly-linked list with a random pointer.
 * struct ListNode {
 *     int val;
 *     ListNode *next, *random;
 *     ListNode(int x) : val(x), next(NULL), random(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *copyRandomList(ListNode *head) {
        ListNode *t = head;
        while(t){
            ListNode *p = new ListNode(t->val);
            p->next = t->next;
            t->next = p;
            t = p->next;
        }
        t = head;
        while(t){
            if(t->random)   t->next->random = t->random->next;
            t = t->next->next;
        }
        ListNode *dummy = new ListNode(-1), *s = dummy;
        t = head;
        while(t){
            s->next = t->next;
            s = t->next;
            t->next = t->next->next;  // 复原
            t = t->next;
        }
        s->next = NULL;
        return dummy->next;

    }
};