teaching machines

CS 245 Lecture 19 – Snake

Agenda

  • what ?s
  • Snake with ArrayList
  • linked structures

TODO

  • I’ve reduced the grading scale by a couple of points. There are still 18 Blugolds available.

Code

HashSet.java

package lecture19;

import java.util.ArrayList;

public class HashSet<T> {
  private ArrayList<T>[] items;
  
  public HashSet() {
    items = new ArrayList[5];
  }
  
  public void add(T item) {
    int i = Math.abs(item.hashCode()) % items.length;
    if (items[i] == null) {
      items[i] = new ArrayList<T>();
    }
    if (!items[i].contains(item)) {
      items[i].add(item);
    }
  }
  
  public void remove(T item) {
    int i = Math.abs(item.hashCode()) % items.length;
    if (items[i] != null) {
      items[i].remove(item);
    }
  }
  
  public boolean contains(T item) {
    int i = Math.abs(item.hashCode()) % items.length;
    return items[i] != null && items[i].contains(item);
  }
  
  public Iterator getIterator() {
    return new Iterator();
  }
  
  public class Iterator {
    private int hashIndexOfItemToRetrieve;
    private int listIndexOfItemToRetrieve;
    
    public Iterator() {
      hashIndexOfItemToRetrieve = 0;
      listIndexOfItemToRetrieve = -1;
      advanceToNextItemToRetrieve();
    }
    
    public boolean hasNext() {
      return hashIndexOfItemToRetrieve < items.length;
    }
    
    public T next() {
      T item = items[hashIndexOfItemToRetrieve].get(listIndexOfItemToRetrieve);
      advanceToNextItemToRetrieve();
      return item;
    }
    
    private void advanceToNextItemToRetrieve() {
      ++listIndexOfItemToRetrieve;
      
      while (hashIndexOfItemToRetrieve < items.length &&
             (items[hashIndexOfItemToRetrieve] == null ||
              listIndexOfItemToRetrieve >= items[hashIndexOfItemToRetrieve].size())) {
        listIndexOfItemToRetrieve = 0;
        ++hashIndexOfItemToRetrieve;
      }
    }
  }
  
  public static void main(String[] args) {
    HashSet<String> set = new HashSet<String>();
    set.add("a");
    System.out.println(set.contains("a"));
    set.remove("a");
    System.out.println(set.contains("a"));
    
    set.add("a");
    set.add("b");
    set.add("c");
    set.add("d");
    set.add("e");
    set.add("f");
    set.add("g");
    set.add("z");
    set.add("z");
    set.add("ifrim");
    set.add("racecar");
    
    System.out.println(set.contains("racecar"));
    System.out.println(set.contains("tacocat"));
    
    HashSet<String>.Iterator i = set.getIterator();
    while (i.hasNext()) {
      System.out.println(i.next());
    }
  }
}

SnakesOnAFrame.java

package lecture19;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class SnakesOnAFrame extends JFrame implements KeyListener {
  private static final int TILE_WIDTH = 25;
  private static final int TILE_HEIGHT = 25;
  private int heightInTiles;
  private int widthInTiles;
  private SnakesPanel panel;
  private ArrayList<Point> snake;

  private HashSet<Point> eggs;

  public SnakesOnAFrame() {
    eggs = new HashSet<Point>();

    panel = new SnakesPanel();
    add(panel);

    setFocusable(true);
    requestFocusInWindow();
    addKeyListener(this);

    setSize(1024, 600);

    heightInTiles = (int) (getSize().getHeight() / TILE_HEIGHT);
    widthInTiles = (int) (getSize().getWidth() / TILE_WIDTH);

    generateEggs();
    snake = new ArrayList<Point>();
    snake.add(new Point(6, 9));

    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
  }

  private void generateEggs() {
    Random g = new Random();
    for (int i = 0; i < 20; ++i) {
      int y = g.nextInt(heightInTiles);
      int x = g.nextInt(widthInTiles);
      eggs.add(new Point(x, y));
    }
  }

  class SnakesPanel extends JPanel {
    public void paintComponent(Graphics g) {
      super.paintComponent(g);

      // draw eggs
      g.setColor(Color.ORANGE);
      HashSet<Point>.Iterator i = eggs.getIterator();
      while (i.hasNext()) {
        Point egg = i.next();
        g.fillOval(egg.x * TILE_WIDTH, egg.y * TILE_HEIGHT, TILE_WIDTH, TILE_HEIGHT);
      }

      g.setColor(Color.GREEN);
      for (Point segment : snake) {
        g.fillRoundRect(segment.x * TILE_WIDTH, segment.y * TILE_HEIGHT, TILE_WIDTH, TILE_HEIGHT, 5, 5);
      }
    }
  }

  public static void main(String[] args) {
    new SnakesOnAFrame();
  }

  @Override
  public void keyPressed(KeyEvent arg0) {
  }

  @Override
  public void keyReleased(KeyEvent event) {
    Point head = new Point(snake.get(0));
    switch (event.getKeyCode()) {
      case KeyEvent.VK_UP:
        --head.y;
        break;
      case KeyEvent.VK_DOWN:
        ++head.y;
        break;
      case KeyEvent.VK_LEFT:
        --head.x;
        break;
      case KeyEvent.VK_RIGHT:
        ++head.x;
        break;
    }

    snake.add(0, head);

    // Is there an egg under the head?
    if (!eggs.contains(head)) {
      snake.remove(snake.size() - 1);
    } else {
      eggs.remove(head);
    }

    panel.repaint();
  }

  @Override
  public void keyTyped(KeyEvent arg0) {
  }
}

Haiku

An ID crisis
Am I male? What is a train?
Array or linked list?

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