package brs.visitor;

import brs.*;

/**
* An object-oriented leaf counter.  Uses anonymous inner classes to "help" count
* the leaves of a BiTree host.
*@author Dung X. Nguyen - Copyright 2000 - All rights reserved.
*/
public class LeafCounter implements IVisitor
{
	public final static LeafCounter Singleton = new LeafCounter ();

	private LeafCounter ()
	{
	}

	/**
	 * Returns 0 - empty tree has no leaf.
	 * @param host
	 * @param notUsed not needed.
	 * @return Integer (0).
	 */
	public Object emptyCase (BiTree host, Object notUsed)
	{
		return new Integer (0);
	}

	/**
	 * Asks the subtrees to "help" count the leaves.
	 * @param host
	 * @param notUsed not needed.
	 * @return the number of leaves in the host.
	 */
	public Object nonEmptyCase (BiTree host, Object notUsed)
	{
      // passes the right subtree to the left subtree and asks it to help count the  leaves.
		return host.getLeftSubTree().execute (
         new IVisitor ()
         {
            public Object emptyCase (BiTree h, Object hSib)
            // asks the sibling subtree of h, hSib, to "help" count.
            {
               return ((BiTree)hSib).execute (
                  new IVisitor ()
                  {
                     public Object emptyCase (BiTree st, Object inpNotUsed)
                     // host is a leaf, and the leaf count is 1.
                     {
                        return new Integer (1);
                     }

                     public Object nonEmptyCase (BiTree st, Object inpNotUsed)
                     // the leaf count is just the leaf count of hSib (i.e. st).
                     {
                        return st.execute (LeafCounter.Singleton, null);
                     }
                  }
                  , null);
            }

            public Object nonEmptyCase (BiTree h, Object hSib)
            // host's leaf count is the sum of the subtrees' leaf count.
            {
               Integer hCount = (Integer)h.execute (LeafCounter.Singleton, null);
               Integer sibCount = (Integer)((BiTree)hSib).execute (LeafCounter.Singleton, null);
               return new Integer (hCount.intValue () + sibCount.intValue ());
            }
         }
         , host.getRightSubTree ());
	}

	/**
	 * @param args == null - not used.
	 */
	public static void main(String[] args)
	{
      Integer level0 = new Integer (0);
      BiTree t0 = new BiTree ();
      System.out.println ("t0 is:\n " + t0);
      System.out.println("\nt0 leaf count is: " + t0.execute(LeafCounter.Singleton, null));
      t0.insertRoot (new Integer (5));
      BiTree t1 = new BiTree ();
      t1.insertRoot (new Integer (-7));
      BiTree t2 = new BiTree ();
      t2.insertRoot (new Integer (3));
      System.out.println ("\nt2 is:\n" + t2);
      System.out.println("\nt2 leaf count is: " + t2.execute(LeafCounter.Singleton, null));
      t1.setLeftSubTree(t0);
      System.out.println ("\nt1 is:\n " + t1);
      System.out.println("\nt1 leaf count is: " + t1.execute(LeafCounter.Singleton, null));
      t1.setRightSubTree (t2);
      System.out.println ("\nt1 is:\n " + t1);
      System.out.println("\nt1 leaf count is: " + t1.execute(LeafCounter.Singleton, null));
	}

}