package algs13;
import stdlib.*;
/* ***********************************************************************
 *  Compilation:  javac ZLinkedStackOfStrings.java
 *  Execution:    java ZLinkedStackOfStrings
 *
 *  A stack of strings, implemented using a linked list.
 *
 *  % more tobe.txt
 *  to be or not to - be - - that - - - is
 *
 *  % java ZLinkedStackOfStrings < tobe.txt
 *  to be not that or be
 *
 *************************************************************************/

public class XStackOfStrings {
	private int N;          // size of the stack
	private Node first;     // top of stack

	// helper Node class
	private static class Node {
		public Node() { }
		public String item;
		public Node next;
	}

	// is the stack empty?
	public boolean isEmpty() { return first == null; }

	// number of elements on the stack
	public int size() { return N; }


	// add an element to the stack
	public void push(String item) {
		Node oldfirst = first;
		first = new Node();
		first.item = item;
		first.next = oldfirst;
		N++;
	}

	// delete and return the most recently added element
	public String pop() {
		if (isEmpty()) throw new Error("Stack underflow");
		String item = first.item;      // save item to return
		Node oldfirst = first;
		first = first.next;            // delete first node
		N--;
		return item;                   // return the saved item
	}

	// test client
	public static void main(String[] args) {
//		Trace.run ();
//		Trace.drawStepsOfMethod ("push");
//		Trace.drawStepsOfMethod ("pop");
		StdIn.fromString ("to be or not to - be - - that - - - is");

		XStackOfStrings s = new XStackOfStrings();
		while (!StdIn.isEmpty()) {
			String item = StdIn.readString();
			Trace.draw ();
			if (!item.equals("-")) s.push(item);
			else if (s.isEmpty())  StdOut.println("BAD INPUT");
			else                   StdOut.print(s.pop() + " ");
		}
	}


}