Initial data commit

Task/Sierpinski-pentagon/Java/sierpinski-pentagon.java

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+import java.awt.*;
+import java.awt.event.ActionEvent;
+import java.awt.geom.Path2D;
+import static java.lang.Math.*;
+import java.util.Random;
+import javax.swing.*;
+
+public class SierpinskiPentagon extends JPanel {
+    // exterior angle
+    final double degrees072 = toRadians(72);
+
+    /* After scaling we'll have 2 sides plus a gap occupying the length
+       of a side before scaling. The gap is the base of an isosceles triangle
+       with a base angle of 72 degrees. */
+    final double scaleFactor = 1 / (2 + cos(degrees072) * 2);
+
+    final int margin = 20;
+    int limit = 0;
+    Random r = new Random();
+
+    public SierpinskiPentagon() {
+        setPreferredSize(new Dimension(640, 640));
+        setBackground(Color.white);
+
+        new Timer(3000, (ActionEvent e) -> {
+            limit++;
+            if (limit >= 5)
+                limit = 0;
+            repaint();
+        }).start();
+    }
+
+    void drawPentagon(Graphics2D g, double x, double y, double side, int depth) {
+        double angle = 3 * degrees072; // starting angle
+
+        if (depth == 0) {
+
+            Path2D p = new Path2D.Double();
+            p.moveTo(x, y);
+
+            // draw from the top
+            for (int i = 0; i < 5; i++) {
+                x = x + cos(angle) * side;
+                y = y - sin(angle) * side;
+                p.lineTo(x, y);
+                angle += degrees072;
+            }
+
+            g.setColor(RandomHue.next());
+            g.fill(p);
+
+        } else {
+
+            side *= scaleFactor;
+
+            /* Starting at the top of the highest pentagon, calculate
+               the top vertices of the other pentagons by taking the
+               length of the scaled side plus the length of the gap. */
+            double distance = side + side * cos(degrees072) * 2;
+
+            /* The top positions form a virtual pentagon of their own,
+               so simply move from one to the other by changing direction. */
+            for (int i = 0; i < 5; i++) {
+                x = x + cos(angle) * distance;
+                y = y - sin(angle) * distance;
+                drawPentagon(g, x, y, side, depth - 1);
+                angle += degrees072;
+            }
+        }
+    }
+
+    @Override
+    public void paintComponent(Graphics gg) {
+        super.paintComponent(gg);
+        Graphics2D g = (Graphics2D) gg;
+        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
+                RenderingHints.VALUE_ANTIALIAS_ON);
+
+        int w = getWidth();
+        double radius = w / 2 - 2 * margin;
+        double side = radius * sin(PI / 5) * 2;
+
+        drawPentagon(g, w / 2, 3 * margin, side, limit);
+    }
+
+    public static void main(String[] args) {
+        SwingUtilities.invokeLater(() -> {
+            JFrame f = new JFrame();
+            f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+            f.setTitle("Sierpinski Pentagon");
+            f.setResizable(true);
+            f.add(new SierpinskiPentagon(), BorderLayout.CENTER);
+            f.pack();
+            f.setLocationRelativeTo(null);
+            f.setVisible(true);
+        });
+    }
+}
+
+class RandomHue {
+    /* Try to avoid random color values clumping together */
+    final static double goldenRatioConjugate = (sqrt(5) - 1) / 2;
+    private static double hue = Math.random();
+
+    static Color next() {
+        hue = (hue + goldenRatioConjugate) % 1;
+        return Color.getHSBColor((float) hue, 1, 1);
+    }
+}