/********************************************/
/* Simulation of Monty Hall problem         */
/* In a gameshow there are three doors. Two */
/* doors each hide a goat. Behind the third */
/* there's a car. After the candidate has   */
/* picked one door (but not opened it), the */
/* quizmaster (who knows what's behind the  */
/* doors) opens one of the other doors and  */
/* shows a goat behind it. The candidate    */
/* is then allowed to choose another door.  */
/* This simulation demonstrates the chances */
/* in case the candidate changes his mind.  */
/********************************************/

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
public class EngMontyHall extends Applet implements Runnable, MouseListener {
   int b, h, fontSize, doorWithCar, firstChoice, newChoice, stringLength, started,
      noOfShows, i, x, y, incr, openedByQM, noOfCarsWon, door[] = new int[4];
   boolean begin;   
   final int goat=0, car=1, maxShows=1000000;
   private Thread thread;
   Image im;
   Graphics gIm;

   public void init () {
      addMouseListener (this);
      Dimension d = getSize();
      b = d.width; h = d.height; // width and height of applet window
      x = b/15; y = h/6; incr = 44;
      setBackground (Color.black);
   }

   public void start () {
      if (thread == null) {
         thread = new Thread (this);
         thread.start();
      }
   }

   public void stop () {
      if (thread != null) {
         thread.stop();
         thread = null;
      }
   }

   public void paint (Graphics g) {
      if (begin) {
         if (noOfShows < maxShows) {
            noOfShows++;

         /***  FIRST HIDE CAR AND TWO  ***/
         /*** GOATS BEHIND THREE DOORS ***/

            doorWithCar = 1 + (int)(3 * Math.random());
            door[doorWithCar] = car;
            for (i=1; i<=3; i++)
               if (i != doorWithCar)
                  door[i] = goat;
      
         /*** CANDIDATE PICKS ONE DOOR ***/

            firstChoice = 1 + (int)(3 * Math.random());

         /*** QUIZMASTER OPENS OTHER DOOR,  ***/
         /*** BEHIND WHICH THERE IS A GOAT. ***/

            do
               openedByQM = 1 + (int)(3 * Math.random());
            while (door[openedByQM]==car || openedByQM==firstChoice);
      
         /*** THEN CANDATE IS GIVEN THE    ***/
         /*** CHANCE TO CHOOSE OTHER DOOR. ***/
   
            for (i=1; i<=3; i++)
               if (i != firstChoice && i != openedByQM)
                  newChoice = i;
        
         /*** FINALLY 1 IS ADDED TO NUMBER OF CARS  ***/
         /*** IF DOOR CHOSEN APPEARS TO REVEAL CAR. ***/
   
            if (door[newChoice] == car)
               noOfCarsWon++;
         }
         if (noOfShows%100 == 0 || noOfShows<=1000 && noOfShows%10 == 0) {
            if (im == null) {
               im = createImage (b, h);
               gIm = im.getGraphics();
            }
            String s = "Number of cars won per show:";
            fontSize = bepaalFont (g, 5*b/9, s);
            Font f = new Font("Verdana", Font.PLAIN, fontSize);
            introScreen (gIm);
            FontMetrics fm = getFontMetrics(f);
            stringLength = fm.stringWidth(s);
            gIm.setColor (Color.yellow);
            gIm.setFont (new Font("Verdana", Font.BOLD, fontSize));
            gIm.drawString ("The Monty Hall problem", x, y);
            gIm.setFont (f);
            gIm.drawString ("Number of shows:", x, y+incr);
            gIm.drawString ("Number of cars won:", x, y+2*incr);
            gIm.drawString (s, x, y+3*incr);
            gIm.setColor (Color.black);
            gIm.fillRect (x+stringLength+1, y+h/20, 2*b/9, 2*h/3);
            gIm.setFont (new Font("Verdana", Font.PLAIN, fontSize));
            gIm.setColor (Color.yellow);
            gIm.drawString (""+noOfShows, x+stringLength+10, y+incr);
            gIm.drawString (""+noOfCarsWon, x+stringLength+10, y+2*incr);
            gIm.drawString (format((double)noOfCarsWon/noOfShows), x+stringLength+10, y+3*incr);
            if (noOfShows == maxShows)
               gIm.drawString ("== Click for new simulation ==",x,h-fontSize-10);
            if (im != null)
               g.drawImage (im, 0, 0, null);
         }
      }
      else {
         if (im == null) {
            im = createImage (b, h);
            gIm = im.getGraphics();
         }
         introScreen(gIm);
         String s = "The Monty Hall problem";
         fontSize = bepaalFont (g, 2*b/3, s);
         Font f = new Font("Verdana", Font.PLAIN, fontSize);
         gIm.setFont (f);
         gIm.setColor (Color.yellow);
         gIm.setFont (new Font("Verdana", Font.BOLD, fontSize));
         gIm.drawString (s, x, y+incr);
         if (im != null)
            g.drawImage (im, 0, 0, null);
      }
   }

   void introScreen (Graphics g) {
      g.setColor (Color.black);
      g.fillRect (0,0,b,h);
      g.setColor (Color.green);
      for (i=0;i<5;i++)
         g.drawRoundRect (i,i,b-2*i,h-2*i,5,5);
   }

   public void run () {
      for (;;) {
         repaint();
      }
   }

   public void update (Graphics g) {
      paint(g);
   }

   int bepaalFont (Graphics g, int breedte, String s) {
      FontMetrics fm;
      int fontSize = 5, stringWidth;
      do {
         fontSize++;
         g.setFont (new Font ("Arial",Font.PLAIN,fontSize));
         fm = g.getFontMetrics();
         stringWidth = fm.stringWidth(s);
      } while (stringWidth < breedte);
      return fontSize - 1;
   }

   String format (double d) {
     long tmp = (long)(10000 * d + 0.05);
     return ""+(double)tmp/10000;

   }
   public void mousePressed (MouseEvent evt) {
      if (noOfShows == 0 || noOfShows == maxShows) {
         begin = true;
         noOfShows = noOfCarsWon = 0;
      }
   }

   public void mouseReleased (MouseEvent evt){}
   public void mouseEntered (MouseEvent evt){}
   public void mouseExited (MouseEvent evt){}
   public void mouseClicked (MouseEvent evt){}
}