Task: Brownian tree
C: #include <string.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <FreeImage.h>

#define NUM_PARTICLES  1000
#define SIZE           800

void draw_brownian_tree(int world[SIZE][SIZE]){
  int px, py; 
  int dx, dy; 
  int i;
 
  
  world[rand() % SIZE][rand() % SIZE] = 1;

  for (i = 0; i < NUM_PARTICLES; i++){
    
    px = rand() % SIZE;
    py = rand() % SIZE;

    while (1){
      
      dx = rand() % 3 - 1;
      dy = rand() % 3 - 1;

      if (dx + px < 0 || dx + px >= SIZE || dy + py < 0 || dy + py >= SIZE){
        
        px = rand() % SIZE;
        py = rand() % SIZE;
      }else if (world[py + dy][px + dx] != 0){
        
        world[py][px] = 1;
        break;
      }else{
        py += dy;
        px += dx;
      }
    }
  }
}

int main(){
  int world[SIZE][SIZE];
  FIBITMAP * img;
  RGBQUAD rgb;
  int x, y;
 
  memset(world, 0, sizeof world);
  srand((unsigned)time(NULL));

  draw_brownian_tree(world);

  img = FreeImage_Allocate(SIZE, SIZE, 32, 0, 0, 0);

  for (y = 0; y < SIZE; y++){
    for (x = 0; x < SIZE; x++){
      rgb.rgbRed = rgb.rgbGreen = rgb.rgbBlue = (world[y][x] ? 255 : 0);
      FreeImage_SetPixelColor(img, x, y, &rgb);
    }
  }
  FreeImage_Save(FIF_BMP, img, "brownian_tree.bmp", 0);
  FreeImage_Unload(img);
}

Java: import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.util.*;
import javax.swing.JFrame;

public class BrownianTree extends JFrame implements Runnable {

    BufferedImage I;
    private List<Particle> particles;
    static Random rand = new Random();

    public BrownianTree() {
        super("Brownian Tree");
        setBounds(100, 100, 400, 300);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        I = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB);
        I.setRGB(I.getWidth() / 2, I.getHeight() / 2, 0xff00);
        particles = new LinkedList<Particle>();
    }

    @Override
    public void paint(Graphics g) {
        g.drawImage(I, 0, 0, this);
    }

    public void run() {
        for (int i = 0; i < 20000; i++) {
            particles.add(new Particle());
        }
        while (!particles.isEmpty()) {
            for (Iterator<Particle> it = particles.iterator(); it.hasNext();) {
                if (it.next().move()) {
                    it.remove();
                }
            }
            repaint();
        }
    }

    public static void main(String[] args) {
        BrownianTree b = new BrownianTree();
        b.setVisible(true);
        new Thread(b).start();
    }

    private class Particle {

        private int x, y;

        private Particle() {
            x = rand.nextInt(I.getWidth());
            y = rand.nextInt(I.getHeight());
        }

        
        private boolean move() {
            int dx = rand.nextInt(3) - 1;
            int dy = rand.nextInt(3) - 1;
            if ((x + dx < 0) || (y + dy < 0)
                    || (y + dy >= I.getHeight()) || (x + dx >= I.getWidth())) {
                return true;
            }
            x += dx;
            y += dy;
            if ((I.getRGB(x, y) & 0xff00) == 0xff00) {
                I.setRGB(x - dx, y - dy, 0xff00);
                return true;
            }
            return false;
        }
    }
}