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

namespace Stacks
{
    class Stack<T>
    {
        private Node<T> head;

        public Stack()
        {
            head = null;
        }

        public bool isEmpty()
        {
            return head == null;
        }

        public void push(T x)
        {
            head = new Node<T>(x, head);
        }

        public T pop()
        {
            if (isEmpty())
                return default(T);

            T val = head.getValue();

            head = head.getNext();

            return val;
        }

        public T top()
        {
            if (isEmpty())
                return default(T);

            return head.getValue();
        }

        public override string ToString()
        {
            string baseStr = "[";

            while (!isEmpty())
            {
                if (baseStr.Length > 1)
                    baseStr += ", ";

                baseStr += pop().ToString();
            }

            baseStr += "]";

            return baseStr;
        }
    }
}