import java.util.Iterator; import java.util.NoSuchElementException; import java.util.Scanner; public class Stack<Item> implements Iterable<Item> { private int N; private Node<Item> first; private static class Node<Item> { private Item item; private Node<Item> next; } public Stack() { first = null; N = 0; } public boolean isEmpty() { return first == null; } public int size() { return N; } public void push(Item item) { Node<Item> oldfirst = first; first = new Node<Item>(); first.item = item; first.next = oldfirst; N ++; } public Item pop() { if(isEmpty()) throw new NoSuchElementException("Stack underflow"); Item item = first.item; first = first.next; N --; return item; } public Item peek() { if(isEmpty()) throw new NoSuchElementException("Stack underflow"); return first.item; } public String toString() { StringBuilder s = new StringBuilder(); for(Item item : this) s.append(item + " "); return s.toString(); } public Iterator<Item> iterator() { return new ListIterator<Item>(first); } private class ListIterator<Item> implements Iterator<Item> { private Node<Item> current; public ListIterator(Node<Item> first) { current = first; } public boolean hasNext() { return current != null; } public void remove() { throw new UnsupportedOperationException(); } public Item next() { if(!hasNext()) throw new NoSuchElementException(); Item item = current.item; current = current.next; return item; } } public static void main(String[] args) { Stack<String> s = new Stack<String>(); Scanner in = new Scanner(System.in); while(in.hasNext()) { String item = in.next(); if(!item.equals("-")) s.push(item); else if(!s.isEmpty()) System.out.println(s.pop() + " "); System.out.println("(" + s.size() + " left on stack)"); } } } |
