using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    public static void AddLists(Node h1, Node h2)

    {

        Node h3 = null;

        var sumData = 0;

        while (h1 != null || h2 != null)

        {

            var sumNode = new Node();

            if (h1 != null)

            {

                sumData += h1.Data;

                h1 = h1.Next;

            }

            if (h2 != null)

            {

                sumData += h2.Data;

                h2 = h2.Next;

            }

            sumNode.Data = sumData % 10;

            if (sumData > sumNode.Data)

            {

                sumData = 1;

            }

            else

            {

                sumData = 0;

            }

            if (h3 != null)

            {

                h3.Next = sumNode;

            }

            h3 = sumNode;

        }

    }

    public static (int, Node) AddListsReverse(Node h1, Node h2)

    {

        var len1 = h1.Length;

        var len2 = h2.Length;

        if (len1 > len2)

        {

            PadList(h2, len1 - len2);

        }

        else if (len1 < len2)

        {

            PadList(h2, len2 - len1);

        }

        if (h1 == null)

            return (0, null);

        var result = AddListsReverse(h1.Next, h2.Next);

        var sum = result.Item1 + h1.Data + h2.Data;

        var node = new Node();

        node.Data = sum % 10;

        node.Next = result.Item2;

        return (sum >= 10 ? 1 : 0, node);

    }

    // must return new head

    public static Node PadList(Node head, int numOfNodes)

    {

        for (int i = 0; i < numOfNodes; i++)

        {

            var node = new Node();

            node.Next = head;

            head = node;

        }

        return head;

    }

}

​

public class Node

{

    public Node Next {get; set;}

    public int Data {get; set;}

    public int Length {get; set;}

}