using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var head = FillWith(9559,2125);

        Print(head);

        Console.WriteLine("REVERSE");

        var revers = Add(head);

        Print(revers);

        Console.WriteLine("Forward");

        var forward = AddForward(head);

        Print(forward);

    }

    public static Node FillWith( int number, int number2)

    {

        if(number == 0) return null;

        var temp = new Node(){

            Digit = number %10,

            Digit1 = number2 %10

        };

        temp.Next = FillWith(number /10, number2/10);

        return temp;

    }

    public static void Print(Node n)

    {

        if(n == null) return;

        Console.WriteLine("{0} -- {1}",n.Digit, n.Digit1);

        Print(n.Next);

    }

    public static Node Add(Node n, int res =0)

    {

        if( n== null) return res == 0 ? null : new Node() { Digit = res};

        var node = new Node();

        var result = (n.Digit + n.Digit1 + res);

        node.Digit = result%10;

        node.Next = Add(n.Next, result /10);

        return node;

    }

    public static Node AddForward(Node n)

    {

        var res =0;

        var head = AddInnerForward(n, out res);

        if(res >0)

        {

            var temp = new Node(){ Digit = res};

            temp.Next = head;

            head = temp;

        }

        return head;        

    }

    public static Node AddInnerForward(Node n, out int res)

    {

        var node = new Node();

        if(n.Next == null) {

            var klk = n.Digit + n.Digit1;

            res = klk/10;

            node.Digit = klk %10;

            return node;

        };

        node.Next = AddInnerForward(n.Next, out res);

        var result = (n.Digit + n.Digit1 + res);

        node.Digit = result %10;

        res = result /10;

        return node;

    }

}

​

public class Node {

    public Node Next;

    public int Digit;

    public int Digit1;  

}