//Permutations.java


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


public class Permutations extends JApplet {

    JTextField inputNField;
    JTextField outputPField;
    JTextArea listArea;
    JLabel errorLabel;

    java.util.List permsList;


    public void init() {
	Container container = getContentPane();
	int panelRowsSize = 2;
	container.setLayout( new GridLayout( 1, panelRowsSize) );

	JPanel [] panelRows = new JPanel[panelRowsSize];

	//left side panel
	panelRows[0] = new JPanel();
	container.add( panelRows[0] );
	panelRows[0].setLayout( new FlowLayout() );

	//right side panel
	panelRows[1] = new JPanel();
	panelRows[1].setLayout( new FlowLayout() );
	container.add( panelRows[1] );

	permsList = new ArrayList();

	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 );

	outputPField = new JTextField( 6 );
	outputPField.setFont( bigFont );
	outputPField.setEditable( false );
	panelRows[0].add( outputPField );


	errorLabel = new JLabel( "" );
	panelRows[0].add( errorLabel );


	listArea = new JTextArea( 16, 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 ) {

	    listArea.setText( "" );		    
	    errorLabel.setText( "" );
	    outputPField.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;
            }
	    if ( n > 14 ) {
		errorLabel.setText( "up to 14 only" );
		return;
	    }
                                                          
	    StringBuffer L= new StringBuffer(" abcdefghijklmn");    //14 chars
 
	    permsList.clear();

	    perms ( L, 1, n );

	    outputPField.setText( "" + permsList.size() );	    
	    
	    Iterator it = permsList.iterator();
	    while ( it.hasNext() )
		listArea.append( (String)it.next() + "\n" );

	}
    }
    


    //permutations from k to N
    void perms ( StringBuffer L, int k, int n) {

	char temp;
	
	if (k == n)    //N to N
	    permsList.add( L.substring( 1, n+1 ) );

	else
	    for (int i=k; i<=n; i++) {  //for each I from k to N
		temp = L.charAt(i);        //swap with Kth
		L.setCharAt( i, L.charAt(k) );
		L.setCharAt( k, temp );
		//recurse to find permutations from K+1 to N in copy of String
		perms( new StringBuffer( L.toString() ), k+1, n);  
	    }
    }
    
    
}