给定一个链表，每个节点包含一个额外增加的随机指针，该指针可以指向链表中的任何节点或空节点。
要求返回这个链表的深度拷贝。

代码

class Solution {
public:
    RandomListNode *copyRandomList(RandomListNode *head) {
        if (!head) return NULL;
        RandomListNode *res = new RandomListNode(head->label);
        RandomListNode *node = res;
        RandomListNode *cur = head->next;
        map<RandomListNode*, RandomListNode*> m;
        m[head] = res;
        while (cur) {
            RandomListNode *tmp = new RandomListNode(cur->label);
            node->next = tmp;
            m[cur] = tmp;
            node = node->next;
            cur = cur->next;
        }
        node = res;
        cur = head;
        while (node) {
            node->random = m[cur->random];
            node = node->next;
            cur = cur->next;
        }
        return res;
    }
};