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class Solution {
    public Node copyRandomList(Node head) {
        if (head == null) {
            return null;
        }

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

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

        Node dummy = new Node(0);
        Node copyCur = dummy;

        cur = head;
        while (cur != null) {
            Node copy = cur.next;
            Node nextOld = copy.next;

            copyCur.next = copy;
            copyCur = copy;

            cur.next = nextOld;
            cur = nextOld;
        }

        return dummy.next;
    }
}