using System;

public class Program

{

    public static void Main()

    {

        var items = new Dequeue(10);

        items.AddLeft(1);

        items.AddLeft(2);

        items.AddLeft(3);

        for (var index = 0; index < 10; index++)

        {

            Console.WriteLine($"{index}:{items[index]}");

        }

    }

}

​

public class Dequeue

{

    private int[] _items;

    private int _head;

    private int _tail;

    private int _count;

    public Dequeue()

        : this(100)

    {

    }

    public Dequeue(int capacity)

    {

        _items = new int[capacity];

    }

    public int this[int index]

    {

        get

        {

            return _items[index];

        }

    }

    public bool IsEmpty()

    {

        return _count == 0;

    }

    public bool IsFull()

    {

        return _count == _items.Length;

    }

    public void AddLeft(int value)

    {

        if (IsFull())

        {

            Resize(_items.Length * 2);

        }

        _head = _head <= 0 ? _items.Length - 1 : _head - 1;

        _items[_head] = value;

        _count += 1;

    }

    public void AddRight(int value)

    {

        if (IsFull())

        {

            Resize(_items.Length * 2);

        }

        _tail = _tail >= _items.Length ? 0 : _tail + 1;

        _items[_tail] = value;

        _count += 1;

    }

    private void Resize(int capacity)

    {

    }

}