/*

* Sample usage: java LinkedStack < tobe.txt

*/

import java.util.Iterator;

public class LinkedStack<Item> implements Iterable<Item> {

private Node first; // top of stack (most recently added node)

private int N; // number of items

private class Node{

// nested class to define nodes

Item item;

Node next;

}

public boolean isEmpty(){

return first == null;

} // Or: N == 0.

public int size(){

return N;

}

public void push(Item item){

// Add item to top of stack.

Node oldFirst = first;

first = new Node();

first.item = item;

first.next = oldFirst;

N++;

}

public Item pop(){

// Remove item from top of stack.

Item item = first.item;

first = first.next;

N--;

return item;

}

public Iterator<Item> iterator(){

return new ListIterator();

}

private class ListIterator implements Iterator<Item>{

private Node current = first;

public boolean hasNext(){

return current != null;

}

public Item next(){

Item item = current.item;

current = current.next;

return item;

}

public void remove(){ }

}

public static void main(String[] args){

LinkedStack<String> s;

s = new LinkedStack<String>();

while (!StdIn.isEmpty()){

String item = StdIn.readString();

if (!item.equals("-")){

s.push(item);

}

else if (!item.isEmpty()){

StdOut.print(s.pop()+" ");

}

}

StdOut.println("("+s.size()+" left in stack)");

}

}