using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace List
{

    class LinkedList<T>
    {
        #region [Private members]

        private class Node<T>
        {
            public Node(T key)
            {
                Key = key;
                Prev = null;
                Next = null;
            }

            public T Key { get; set; }
            public Node<T> Prev { get; set; }
            public Node<T> Next { get; set; }
        }

        private Node<T> root;

        private int count;

        private Node<T> At(int index)
        {
            if (index < 0 || index >= Count)
                return null;
            var node = root;
            for (int i = 0; i < index; ++i)
                node = node.Next;
            return node;
        }

        #endregion

        #region [Public members]

        public LinkedList()
        {
            root = null;
        }

        public void Clear()
        {
            root = null;
            count = 0;
        }

        public int Count
        {
            get { return count; }
        }

        public bool Contains(T key)
        {
            for (var x = root; x != null; x = x.Next)
                if (x.Key.Equals(key))
                    return true;
            return false;
        }

        public void Insert(T key, int index)
        {
            var node = new Node<T>(key);

            var prev = At(index - 1);
            if (prev == null)
            {
                node.Next = root;
                root = node;
                ++count;
                return;
            }

            var next = prev.Next;

            if (prev != null)
            {
                prev.Next = node;
                node.Prev = prev;
            }
            if (next != null)
            {
                next.Prev = node;
                node.Next = next;
            }
            ++count;
        }

        public void Add(T key)
        {
            Insert(key, Count);
        }

        public void RemoveAt(int index)
        {
            var node = At(index);
            if (node == null)
                return;
            var prev = node.Prev;
            var next = node.Next;
            if (prev != null)
                prev.Next = next;
            if (next != null)
                next.Prev = prev;
            if (root == node)
                root = next;

            --count;
        }

        public void Remove(T key)
        {
            int index = IndexOf(key);
            RemoveAt(index);
        }

        public T this[int index]
        {
            get
            {
                return At(index).Key;
            }
            set
            {
                At(index).Key = value;
            }
        }

        public int IndexOf(T key)
        {
            int index = 0;
            for (var node = root; node != null; node = node.Next)
            {
                if (node.Key.Equals(key))
                    break;
                ++index;
            }
            return index;
        }

        #endregion
    }


    class Program
    {
        static void Main(string[] args)
        {
            LinkedList<int> list = new LinkedList<int>();
            list.Add(5);
            list.Add(6);
            list.Insert(10, 0);
            Console.WriteLine(list[0]);
            Console.WriteLine(list[1]);
            list.RemoveAt(0);
            Console.WriteLine(list[0]);
            Console.WriteLine(list.Count);
        }
    }
}