思路源于

采用一个哈希表，键值对为<原链表的结点，新链表的结点>，第一次遍历原链表结点时只创建新链表的结点，第二次遍历原链表结点时，通过键拿到新链表结点，新链表结点的next指向哈希表中键为原链表结点的next的值，random同理 

/*
// 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 {
    public Node copyRandomList(Node head) {
        Map<Node, Node> oldMapNew = new HashMap<>();

        for (Node cur = head; cur != null; cur = cur.next) {
            Node newNode = new Node(cur.val);
            oldMapNew.put(cur, newNode);
        }
        for (Node cur = head; cur != null; cur = cur.next) {
            Node newNode = oldMapNew.get(cur);
            newNode.next = oldMapNew.get(cur.next);
            newNode.random = oldMapNew.get(cur.random);
        }
        return oldMapNew.get(head);
    }
}