Solution.java

/*
// 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) {
        if (head == null) {
            return null;
        }

        Node cur = head;
        while (cur != null) {
            Node node = new Node(cur.val);
            node.next = cur.next;
            cur.next = node;
            cur = node.next;
        }

        cur = head;
        while (cur != null) {
            cur.next.random = cur.random == null ? null : cur.random.next;
            cur = cur.next.next;
        }

        Node copy = head.next;
        cur = head;
        while (cur != null) {
            Node next = cur.next;
            cur.next = next.next;
            next.next = next.next == null ? null : next.next.next;
            cur = cur.next;
        }
        return copy;
    }
}