using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public class Stack<T>

    {

        private class Elemento

        {

            T elem;

            bool prioritario;

        }

​

        private List<T> stack = new List<T>();

        private List<T> stackP = new List<T>();

        private bool isEmpty = true;

        private int count = 0;

        private object top = null;

​

​

        public bool IsEmpty

        { get { return isEmpty; } }

​

        public int Count

        { get { return count; } }

​

​

        private void PushAuxiliar(List<T> st, T obj)

        {

            st.Add(obj);

            count++;

            top = obj;

            if (isEmpty)

                isEmpty = false;

        }

​

        public void PushPrioritaire(T obj)

        {

            PushAuxiliar(stackP, obj);

        }

​

        public void Push(T obj)

        {

            PushAuxiliar(stack, obj);

        }

​

        public bool PrioritaireIsEmpty()

        {

            return stackP.Count == 0;

        }

​

        public T Pop()

        {

            if (!isEmpty)

            {

                List<T> st = stackP.Count == 0 ? stack : stackP;

​

                T element = st.Last();

                st.RemoveAt(st.Count - 1);

                count--;

​

                if (count == 0)

                {

                    isEmpty = true;

                    top = null;

                }

                else { 

                    top = stackP.Count > 0 ? stackP[stackP.Count - 1] : stack[stack.Count - 1];

                }

​

                return element;

            }

            else

                throw new InvalidOperationException();

        }

​

​

        public object Peek()

        {

            if (top == null)

                throw new InvalidOperationException();

            else

                return top;

​

        }

​

​

        public void Clear()

        {

            stack.Clear();

            stackP.Clear();

            top = null;

            isEmpty = true;

            count = 0;

        }

    }

    public static void Main()

    {

        Stack<int> s = new Stack<int>();

        s.Push(10);

        s.PushPrioritaire(55);

        s.Push(44);

        s.Push(77);

        Console.WriteLine("Lista vazia: " + s.IsEmpty);

        Console.WriteLine("Primeiro pop acerta no prioritario " + s.Pop());

        Console.WriteLine("Os outros pops acertam nos normais " + s.Pop());

        Console.WriteLine(s.Pop());

    }

}