微软面试题： LeetCode 138. 复制带随机指针的链表 出现次数：3

#include <bits/stdc++.h>
using namespace std;

class Solution {
public:
    Node* copyRandomList(Node* head)
    {
    //第一步：遍历原链表生成新链表，同时用哈希表 memo 存储原链表和新链表对应节点之间的映射关系；
    //第二步：再次遍历原链表，根据原链表每个节点的随机指针和memo,在维护新链表的随机指针；
        if(head == NULL)
        {
            return NULL;
        }
        unordered_map<Node*,Node*> memo;//原节点--> 对应的新生成节
        Node* copy_head = new Node(head->val);
        memo[head] = copy_head;
        Node* front_ptr = copy_head;
        Node* work_ptr = head->next;
        while (work_ptr != NULL)
        {
            Node* tmp_ptr = new Node(work_ptr->val);
            front_ptr->next = tmp_ptr;
            front_ptr = tmp_ptr;
            memo[work_ptr] =  tmp_ptr;
            work_ptr = work_ptr->next;
        }
        work_ptr = head;
        while (work_ptr != NULL)
        {
            if(work_ptr->random != NULL)
            {
                memo[work_ptr]->random = memo[work_ptr->random]; 
            }
            work_ptr = work_ptr->next;
        }
        return copy_head;
    }
};