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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace Linked_Lists
{
    class Node<T>
    {
        public T Data { get; set; }
        public Node<T> Next { get; set; }
        public Node<T> Prev { get; set; }
    }
 
    class LinkedList<T>
    {
        private Node<T> Head;
        private Node<T> Tail;
        public int Size { get; private set; }
 
        public LinkedList()
        {
            Head = null;
            Tail = null;
            Size = 0;
        }
 
        public void add(T elem)
        {
            Node<T> newNode = new Node<T>() { Data=elem, Next=null, Prev=Tail };
            if (Head == null) //elem is the first element
            {
                Head = newNode;
                Tail = Head;
            }
            else
            {
                Tail.Next = newNode;
                Tail = Tail.Next;
                Tail.Next = null;
            }
            Size++;
        }
 
        public T at(int index)
        {
            if (index >= Size || index < 0)
            {
                throw new IndexOutOfRangeException();
            }
            else
            {
                Node<T> cnt = Head;
                for (; index!=0; index--)
                {
                    cnt = cnt.Next;
                }
                return cnt.Data;
            }
 
        }
 
 
        public void removeValue(T elem)
        {
            remove(indexOf(elem));
        }
 
        public void remove(int index)
        {
            if (index >= Size || index < 0)
            {
                throw new IndexOutOfRangeException();
            }
            else
            {
                Node<T> cnt = Head;
                //Find the deletion point
                for (; index != 0; index--)
                {
                    cnt = cnt.Next;
                }
                //cnt is the node to delete.
                //Three cases to handle, based on where the node is located (head, tail, or middle).
                if (cnt == Head)
                {
                    Head = Head.Next;
                }
                else if (cnt == Tail)
                {
                    Tail = Tail.Prev;
                    Tail.Next = null;
                }
                else
                {
                    cnt.Next.Prev = cnt.Prev;
                    cnt.Prev.Next = cnt.Next;
                    cnt = null;
                }
                Size--;
            }
        }
 
        public int indexOf(T elem)
        {
            int index = -1; //Start at an invalid index. Return this unless we find a match for elem.
 
            Node<T> cnt = Head;
            int cntIndex = 0;
            while (cnt != null)
            {
                if (cnt.Data.Equals(elem))
                {
                    index = cntIndex;
                    cnt = null;
                }
                else
                {
                    cnt = cnt.Next;
                    cntIndex++;
                }
            }
            return index;
        }
 
        ~LinkedList()
        {
            Head = null;
            Tail = null;
        }
    }
}