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/**
 * 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 == NULL) return NULL;
        RandomListNode *nHead = new RandomListNode(head->label);
        RandomListNode *p = head, *q = nHead;
        unordered_map<RandomListNode*, RandomListNode*> hash;
        hash[head] = nHead;
        
        while (p->next) {
            RandomListNode *tmp = new RandomListNode(p->next->label);
            hash[p->next] = tmp;
            q->next = tmp, p = p->next, q = q->next;
        }
        
        p = head;
        while(p) {
            hash[p]->random = hash[p->random];
            p = p->next;
        }
        return nHead;
    }
};