/*
 *  JFLAP - Formal Languages and Automata Package
 * 
 * 
 *  Susan H. Rodger
 *  Computer Science Department
 *  Duke University
 *  August 27, 2009

 *  Copyright (c) 2002-2009
 *  All rights reserved.

 *  JFLAP is open source software. Please see the LICENSE for terms.
 *
 */




package pumping.reg;

import pumping.LemmaMath;
import pumping.RegularPumpingLemma;

/**
 * The regular pumping lemma for <i>L</i> = 
 * {<i>a<sup>n</sup>b<sup>k</sup></i> : <i>n</i> is 
 * odd or <i>k</i> is even}.
 * 
 * @author Chris Morgan
 */
public class AnBk extends RegularPumpingLemma {

	public String getTitle() 
	{
		return "a^n b^k : n is odd or k is even";
	}
	
	public String getHTMLTitle() 
	{
		return "<i>a<sup>n</sup>b<sup>k</sup></i> : <i>n</i> is odd"
        	 + " or <i>k</i> is even.";
	}		
	
	public void setDescription()
    {
		partitionIsValid = true;
    	explanation = "Because this is a regular language, a valid decomposition exists.  If <i>m</i> " + GREATER_OR_EQ +
    			" 3, a <i>y</i> value of \"aa\" or \"bb\" will always pump the string.  At least one of those substrings " +
    			"can be the <i>y</i> value.";
    }
	
	protected void setRange() 
	{
		myRange = new int[]{3, 10};
	}
	
	public void chooseI() 
	{
		i = LemmaMath.flipCoin();
	}

	protected void chooseW() 
	{
		if (m % 2 == 0)
			w = pumpString("a", m-2) + "bb";
		else
			w = "a" + pumpString("b", m);
	}
	
	public void chooseDecomposition()
	{
		int firstB = w.indexOf('b');
		
		//One of these should be valid
		if (firstB == -1 || firstB>=2)
			setDecomposition(new int[] {0, 2});
		else
			setDecomposition(new int[] {firstB, 2});
	}
	
	public boolean isInLang(String s) 
	{
		int a, b;    	    	
    	char[] list = new char[] {'a', 'b'};
    	if (LemmaMath.isMixture(s, list))
    		return false;
    	
    	a = LemmaMath.countInstances(s, 'a');
    	b = LemmaMath.countInstances(s, 'b');
    	if (a%2 == 1 || b%2 == 0)
    		return true;    	    	
        return false;
	}
}