//Partitions.java
//number of partitions of each r subset

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;


public class Partitions extends JApplet {

    JTextField inputNField;
    JTextField outputResultField;
    JLabel errorLabel;
    JTextArea listArea;


    public void init() {
	Container container = getContentPane();
	int panelRowsSize = 3;
	container.setLayout( new GridLayout( panelRowsSize, 1 ) );

	JPanel [] panelRows = new JPanel[panelRowsSize];
	for (int i=0; i<panelRowsSize; i++) {
	    panelRows[i] = new JPanel();
	    panelRows[i].setLayout( new FlowLayout() );
	    container.add( panelRows[i] );
	}

	Font bigFont = new Font( "Monospaced", Font.BOLD, 16 );
	TextFieldHandler handleTextField = new TextFieldHandler();

	JLabel inputNLabel = new JLabel( "N" );
	inputNLabel.setFont( bigFont );
	panelRows[0].add( inputNLabel );

	inputNField = new JTextField( 3 );
	inputNField.setFont( bigFont );
	panelRows[0].add( inputNField );
	inputNField.addActionListener( handleTextField );


	outputResultField = new JTextField( 20 );
	outputResultField.setFont( bigFont );
	outputResultField.setEditable( false );
	panelRows[2].add( outputResultField );


	errorLabel = new JLabel( "" );
	errorLabel.setFont( bigFont );
	panelRows[2].add( errorLabel );


	listArea = new JTextArea( 10, 30 );
        Font smallFont = new Font( "Monospaced", Font.BOLD, 12 );
        listArea.setFont( smallFont );
        JScrollPane listScroll = new JScrollPane( listArea );
        panelRows[1].add( listScroll );
                                                                           
    }


    public void start() {
	inputNField.requestFocusInWindow();
    }


    private class TextFieldHandler implements ActionListener {
        public void actionPerformed( ActionEvent event ) {

	    errorLabel.setText( "" );

	    int n=0;
	    try {
		n = Integer.parseInt( inputNField.getText() );
	    }
	    catch (NumberFormatException e) {
		errorLabel.setText( "integer please" );
		return;
	    }
	    if ( n <= 0 ) {
		errorLabel.setText( "positive integer please" );
		return;
	    }

	    listArea.setText( "" );		    
	    listArea.append( "R   partitions\n" );

	    long totalParts = 0;
	    long parts;
	    for (int r=1; r<=n; r++) {
		parts = partitions(n,r);
		totalParts += parts;
		listArea.append( r + "   " + parts + "\n" );
	    }
	    outputResultField.setText( "" + totalParts );
	}
    }

 
 
    long partitions (int n, int r) {
	if (r == 1)
	    return 1;
	else if (r == n)
	    return 1;
	else
	    return partitions(n-1,r-1) + r * partitions(n-1,r);
    }

}