import java.util.Scanner;

/******************************************************
*  Created by Chad Milburn, November 2007.            *
*  Class created for a CS lab, designed to be a       *
*  learning method similar to the game 20 questions.  *
*  Uses recursion and tree to accomplish this.        *
******************************************************/
public class QNode
{
	private String value;				// Contains question.
	private String name;				// Contains guess (animal).
	private QNode y;				// Yes branch.
	private QNode n;				// No branch.
	
	public static void main(String[] args)
	{
		Scanner in;
		boolean has;
		QNode first = new QNode();		// Create first QNode.
		first.value = "Does it have legs?";	// Add first question.
		first.y = new QNode();			// Create first Y branch.
		first.y.name = "cat";			// Add 'cat'.
		first.n = new QNode();			// Create first N branch.
		first.n.name = "snake";			// Add 'snake'.
		do					// Loop until 'quit' is entered.
		{
			first.branch();
			System.out.println("Play again or quit?");
			in = new Scanner(System.in);
			has = in.nextLine().trim().toLowerCase().contains("quit");
		}
		while(!(has));
		System.out.println("Thanks for playing, have a nice day.");
	}
	
	/*****************************************************************
	*  Recursive method contains a question (value), animal (name),  *
	*  and 2 nodes for answers to the question. If the question      *
	*  is empty, it asks if the animal is (name). Yes returns to     *
	*  base case and starts again. No adds a new animal and          *
	*  question, and 2 new nodes for answers.                        *
	*****************************************************************/
	public void branch()
	{
		Scanner in = new Scanner(System.in);
		String input;
		if(value != null)			// Keep traversing branches.
		{
			System.out.println(value);	// Ask question.
			input = in.nextLine().trim().toLowerCase();
			if (input.contains("yes"))
				y.branch();		// Yes branch.
			else
				n.branch();		// No branch.
		}
		else if(value == null)			// Reached end of branch.
		{
			System.out.println("Is it a/an " + name + "?");	//Guess animal.
			input = in.nextLine().trim().toLowerCase();
			if(input.contains("yes"))	// Animal found. Return to base.
			{
				System.out.println("All your base are belong to us.");
			}
			else				// Guess is incorrect, add new animal.
			{
				System.out.println("I give up.");
				System.out.println("What is your animal?");
				String newName = in.nextLine().trim().toLowerCase();
				System.out.println("What is a question that you "
						+ "would answer no to " + newName + ", but "
						+ "yes to " + name + "?");
				String newQuestion = in.nextLine().trim();
				y = new QNode();
				y.name = name;
				n = new QNode();
				n.name = newName;
				name = null;
				value = newQuestion;
				System.out.println("Your animal, " + newName 
						+ ", has been added to my databanks.");
			}
		}
	}
}