package com.telerikacademy;

import java.util.ArrayList;
import java.util.EmptyStackException;
import java.util.Iterator;
import java.util.List;

public class StackImpl<T> implements Stack<T> {
    private int count;

    private static class Node<T>{
        private T data;
        private Node next;


        private Node(T data){
            this.data = data;
        }
    }

    private Node<T> topElement;


    @Override
    public void push(T elem) {
        Node node = new Node(elem);
        node.next = topElement;
        topElement = node;
        count++;
    }

    @Override
    public T pop() {
        if(topElement == null){
            throw new IllegalArgumentException();
        }
        T data = topElement.data;
        topElement = topElement.next;
        count--;
        return data;
    }

    @Override
    public T peek() {
        if(topElement == null){
            throw new IllegalArgumentException();
        }
        return topElement.data;
    }

    @Override
    public int size() {
        return count;
    }

    @Override
    public boolean isEmpty() {
        return topElement == null;
    }
}