Solution2.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;
        }
        for (Node cur = head; cur != null;) {
            Node node = new Node(cur.val, cur.next);
            cur.next = node;
            cur = node.next;
        }
        for (Node cur = head; cur != null; cur = cur.next.next) {
            if (cur.random != null) {
                cur.next.random = cur.random.next;
            }
        }
        Node ans = head.next;
        for (Node cur = head; cur != null;) {
            Node nxt = cur.next;
            if (nxt != null) {
                cur.next = nxt.next;
            }
            cur = nxt;
        }
        return ans;
    }
}