Sword finger offer 35. replication of complex linked list

Title Description

Knowledge point ：

1. Hashtable   Relevant knowledge points of hash table _jcxj2934 The blog of -CSDN Blog

2. Related knowledge of linked list ：  The finger of the sword Offer 06. Print linked list from end to end _jcxj2934 The blog of -CSDN Blog

The idea and code are as follows ：

  Writing reference leetcode Official answer

/*
// Definition for a Node.
class Node {
    int val;
    Node next;
    Node random;

    public Node(int val) {
        this.val = val;
        this.next = null;
        this.random = null;
    }
}
*/
class Solution {
    HashMap<Node,Node> map = new HashMap<>();
    public Node copyRandomList(Node head) {
        // Through the first next Create a new linked list <1>
        // Give it after you create it random assignment 
        // do random You can go through hash Table to quickly find the new node corresponding to the old node 
        //key  It is an old linked list node ,value Is a new linked list node 
        if(head == null)
        {
            return null;
        }
        // If the node doesn't exist , create <1>
        // stay next It doesn't exist when traversing , So this one if Is to pass next Create all the new linked lists 
        if(!map.containsKey(head))
        {
            Node headnew = new Node(head.val);
            map.put(head,headnew);
            headnew.next = copyRandomList(head.next);
            headnew.random = copyRandomList(head.random);
        }
        // by random Only when you assign a value , Return to new node 
        return map.get(head);
    }
}