哈希

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* next;
    Node* random;
    
    Node(int _val) {
        val = _val;
        next = NULL;
        random = NULL;
    }
};
*/
class Solution {
public:
    Node* copyRandomList(Node* head) {
        if(!head) return head;

        unordered_map<Node*, Node*> hashmap;
        hashmap[NULL] = NULL;
        for(auto p = head; p; p = p -> next)
            hashmap[p] = new Node(p -> val);

        for(auto p = head; p; p = p -> next)
        {
            hashmap[p] -> next = hashmap[p -> next];
            hashmap[p] -> random = hashmap[p -> random];
        }
        return hashmap[head];
    }
};
*/
class Solution {
public:
    Node* copyRandomList(Node* head) {
        if(!head) return head;
        //使用哈希来做一个映射
        unordered_map<Node*, Node*> pos;

        pos[NULL] = NULL;
        //先复制正常的next节点，不复制random节点
        for(auto p = head; p; p = p -> next)
            pos[p] = new Node(p -> val);
        
        //复制指针的指向
        for(auto p = head; p; p = p -> next)
        {
            pos[p] -> next = pos[p -> next];
            pos[p] -> random = pos[p -> random];
        }
        return pos[head];
    }
};
/*
// Definition for a Node.
class Node {
p