using System;

​

public class Program

{

    class ListNode<T>

    {

        public readonly T? Value;

        public readonly ListNode<T>? Next;

        public ListNode(T? value, ListNode<T>? next = null)

        {

            Value = value;

            Next = next;

        }

    }

​

    class ListOfNodes<T>

    {

        public ListNode<T>? First = null;

        ListNode<T>? Current = null;

        public int Count = 0;

        public ListNode<T>? Add(T value, ListNode<T>? current = null)

        {

            if (First == null)

            {

                ListNode<T> node = new(value);

                First = node;

                Current = First;

                Count++;

                return node;

            }

​

            if (Current == First)

            {

                Current = null;

                Count = 0;

                First = Current = Add(value, First);

                return First;

            }

​

            if (current.Next != null)

            {

                ListNode<T> node = new(current.Value, Add(value, current.Next));

                Count++;

                return node;

            }

            else

            {

                ListNode<T> nodeNext = new(value, null);

                ListNode<T> node = new(current.Value, nodeNext);

                Count += 2;

                return node;

            }

        }

​

        public ListOfNodes<T>? AddList(ListOfNodes<T> secondList)

        {

            ListOfNodes<T> newList = new();

            ListNode<T> current = this.First;

            for (int i = 0; i < this.Count; i++)

            {

                newList.Add(current.Value);

                current = current.Next;

            }

​

            current = secondList.First;

            for (int i = 0; i < secondList.Count; i++)

            {

                newList.Add(current.Value);

                current = current.Next;

            }

​

            return newList;

        }

​

        public ListOfNodes<T>? ChangeOn(int indexToChange, T value)

        {

            ListOfNodes<T> list = new();

            ListNode<T> current = First;

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

            {

                list.Add(current.Value);

                current = current.Next;

            }

​

            list.Add(value);

            current = current.Next;

            for (int i = indexToChange + 1; i < Count; i++)

            {

                list.Add(current.Value);

                current = current.Next;

            }

​

            return list;

        }

    }

​

    static void Main()

    {

        ListOfNodes<int> nodes = new ListOfNodes<int>();

        nodes.Add(1);

        nodes.Add(2);

        nodes.Add(3);

        nodes.Add(4);

        nodes.Add(5);

        //test conunction

        {

            ListOfNodes<int> nodes2 = new ListOfNodes<int>();

            nodes2.Add(6);

            nodes2.Add(7);

            nodes2.Add(8);

            nodes2.Add(9);

            nodes2.Add(0);

            ListOfNodes<int> nodes3 = nodes.AddList(nodes2);

            ListNode<int> current = nodes.First;

            for (int i = 0; i < nodes.Count; i++)

            {

                Console.Write(current.Value + " ");

                current = current.Next;

            }

​

            current = nodes2.First;

            Console.WriteLine();

            for (int i = 0; i < nodes2.Count; i++)

            {

                Console.Write(current.Value + " ");

                current = current.Next;

            }

​

            Console.WriteLine();

            current = nodes3.First;

            for (int i = 0; i < nodes3.Count; i++)

            {

                Console.Write(current.Value + " ");

                current = current.Next;

            }

        }

​

        //test replace on index

        {

        //nodes = nodes.ChangeOn(0, 6);

        //ListNode<int> current = nodes.First;

        //for (int i = 0; i < nodes.Count; i++)

        //{

        //    Console.Write(current.Value + " ");

        //    current = current.Next;

        //}

        }

    }

}