Leetcode138（力扣138）：复制带随机指针的链表

思路：遍历一次，先创建好所有节点，将节点和原链表放入哈希表 ，然后再次遍历，将所有结点对应连接

class Solution
{
public:
    Node* copyRandomList(Node* head) 
    {
        if(!head) return head;
        Node* cur=head;
        unordered_map<Node*,Node*> keep;
        while(cur)
        {
            Node* copy=new Node(cur->val);
            keep[cur]=copy;
            cur=cur->next;
        }
        cur=head;
        while(cur)
        {
            keep[cur]->next=keep[cur->next];
            keep[cur]->random=keep[cur->random];
            cur=cur->next;
        }
        return keep[head];
    }
};
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