using System;

using System.Collections.Generic;

​

public class DynamicStack<T>

{

    private class Node

    {

        public T Element

        { get; set; }

​

        public Node PreviousNode

        { get; set; }

​

        public Node(T element)

        {

            this.Element = element;

            this.PreviousNode = null;

        }

        public Node(T element, Node previousNode)

        {

            this.Element = element;

            this.PreviousNode = previousNode;

        }

    }

    private Node tail;

    private int count;

    public DynamicStack()

    {

        this.tail = null;

        this.count = 0;

    }

    public void Push(T item)

    {

        if (this.tail == null)

        {

            this.tail = new Node(item);

        }

        else

        {

            Node newNode = new Node(item, this.tail);

            this.tail = newNode;

        }

        this.count++;

    }

    public T Pop()

    {

        Node removedNode = this.tail;

        if (this.tail == null)

        {

            throw new ArgumentNullException("The node is null");

        }

        count--;

        if (count == 0)

        {

            this.tail = null;

        }

        else

        {

            this.tail = this.tail.PreviousNode;

        }

        return removedNode.Element;

    }

    public T Peek()

    {

        Node highestNode = this.tail;

        if (this.tail == null)

        {

            throw new ArgumentNullException("The node is null");

        }

        return highestNode.Element;

    }

    public int Count()

    {

        return count;

    }

    public void Clear()

    {

        while (count != 0)

        {

            //this.tail = null;

            this.tail = this.tail.PreviousNode;

            count--;

        }

    }

}

​

public class DynamicStackTest

{

    public static void Main()

    {

        DynamicStack<string> pile = new DynamicStack<string>();

        pile.Push("soda");

        pile.Push("chips");

        pile.Push("mineral water");

        pile.Push("chocolate");

        pile.Push("beer");

        Console.WriteLine(pile.Pop());

        Console.WriteLine(pile.Peek());

        Console.WriteLine(pile.Count());

        pile.Clear();

        Console.WriteLine(pile.Count());

        pile.Push("fish");

        pile.Push("tea");

        Console.WriteLine(pile.Count());

        Console.WriteLine(pile.Peek());

        Console.WriteLine(pile.Pop());

        Console.WriteLine(pile.Pop());

        Console.WriteLine(pile.Count());

    }

}

​

/*Create a DynamicStack<T> class to implement dynamically a stack

(like a linked list, where each element knows its previous element and the

stack knows its last element). Add methods for all commonly used

operations like Push(), Pop(), Peek(), Clear() and Count

​

Use singly linked list (similar to the list from the previous task, but only

with a field Previous, without a field Next).

​

DoublyLinkedList<string> shoppingList = new DoublyLinkedList<string>();

        shoppingList.Add("Milk");

        shoppingList.Remove("Milk"); // Empty list

        shoppingList.Add("Honey");

        shoppingList.Add("Olives");

        shoppingList.Add("Water");

        shoppingList[2] = "A lot of " + shoppingList[2];

        shoppingList.Add("Fruits");

        shoppingList.RemoveAt(0); // Removes "Honey" (first)

        shoppingList.RemoveAt(2); // Removes "Fruits" (last)

        shoppingList.Add(null);

        shoppingList.Add("Beer");

        shoppingList.Remove(null);

        Console.WriteLine("We need to buy:");

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

        {

            Console.WriteLine(" - " + shoppingList[i]);

        }

        Console.WriteLine("Position of 'Beer' = {0}",

        shoppingList.IndexOf("Beer"));

        Console.WriteLine("Position of 'Water' = {0}",

        shoppingList.IndexOf("Water"));

        Console.WriteLine("Do we have to buy Bread? " +

        shoppingList.Contains("Bread"));

*/