gistfile1.java

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

public class Sierpinski extends JPanel
{
	private static final int DRAW_LEVEL = 128;
	private static final int RECT_SIZE = 4;

	public static void main(String args[])
	{
		final Sierpinski s = new Sierpinski();

		final JFrame jf = new JFrame("Sierpinski triangle");
		jf.setSize(new Dimension(RECT_SIZE * DRAW_LEVEL + 30, RECT_SIZE * DRAW_LEVEL + 80));
		jf.setLayout(new BorderLayout());
		jf.add(s, BorderLayout.CENTER);
		JSlider slider = new JSlider(SwingConstants.HORIZONTAL, 2, 32, 2);
		slider.addChangeListener(new ChangeListener() {
			public void stateChanged(ChangeEvent ce)
			{
				JSlider js = (JSlider)ce.getSource();
				s.divNumber = js.getValue();
				jf.repaint();
			}
		});
		slider.setPaintTicks(true);
		slider.setMajorTickSpacing(1);
		slider.setMinorTickSpacing(1);
		slider.setPaintLabels(true);
		slider.setSnapToTicks(true);
		jf.add(slider, BorderLayout.NORTH);
		jf.setVisible(true);
		jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}

	public int divNumber = 2;

	public void drawPascal(Graphics g, int level)
	{
		if(level == 0)
		{
			// 何もしない
		}
		else
		{
			int x = ((RECT_SIZE * DRAW_LEVEL + 30) / 2) - ((RECT_SIZE / 2) * level);
			int y = (level - 1) * RECT_SIZE;
			for(int i=0; i<level; i++)
			{
				BigInteger combination = combination((level-1), i);
				if(combination.mod(BigInteger.valueOf(divNumber)).equals(BigInteger.ZERO))
				{
					// 偶数は塗らない
					g.drawRect(x + (i * RECT_SIZE), y, RECT_SIZE, RECT_SIZE);
				}
				else
				{
					// 奇数は塗る
					g.fillRect(x + (i * RECT_SIZE), y, RECT_SIZE, RECT_SIZE);
				}
			}

			drawPascal(g, (level - 1));
		}
	}

	public void paint(Graphics g)
	{
		drawPascal(g, DRAW_LEVEL);
	}

	public BigInteger combination(int n, int k)
	{
		BigInteger bunsi = fact(BigInteger.valueOf(n));
		BigInteger bunbo1 = fact(BigInteger.valueOf(n-k));
		BigInteger bunbo2 = fact(BigInteger.valueOf(k));
		BigInteger bunbo = bunbo1.multiply(bunbo2);

		return bunsi.divide(bunbo);
	}

	public BigInteger fact(BigInteger n)
	{
		if(n.equals(BigInteger.ZERO))
		{
			return BigInteger.ONE;
		}
		else
		{
			return n.multiply(fact(BigInteger.valueOf(n.intValue() - 1)));
		}
	}
}