// 2D site percolation on torus,  Evgeny Demidov  31 Oct 2001
  import java.awt.*;
  import java.awt.event.*;
  public class applet-math-percolation1 extends java.applet.Applet
   implements MouseListener, ItemListener, KeyListener{
    int L = 25,L1, d, w, maxColor = 18, hd, hBut = 30,
      cl[][], np[], maxCl = 100000, periodic = 0;
    double p = .5;
    Image buffImage;     Graphics buffGraphics;
    Color col[];
    boolean painted = false;
    Choice chL,chB;    Label  lbL, lbP;    TextField tfP;
    long generTime;
  
  public void init() {
    w = getSize().width;
    cl = new int[w+1][w];  np = new int [maxCl];
    String s=getParameter("L");
    if (s != null) L = Integer.parseInt(s);
    d = w/L;  hd = w-d; L1 = L+1;
    s=getParameter("p");
    if (s != null) p = Double.valueOf(s).doubleValue();
    col = new Color[maxColor];
    col[0] = Color.red;  col[3] = new Color(0,200,0);  col[6] = Color.blue;
    col[9] = new Color(220,220,0);  col[12] = new Color(0,220,220);
    col[15] = new Color(255,0,255);
    col[1] = new Color(255,150,150);  col[4] = new Color(120,255,120);
    col[7] = new Color(150,150,255);  col[10] = new Color(255,255,120);
    col[13] = new Color(120,255,255); col[16] = new Color(255,150,255);
    for (int i = 0; i < 18; i += 3) col[i+2] = col[i].darker();
    buffImage = createImage(w, w);   buffGraphics = buffImage.getGraphics();
    addMouseListener(this);
    chL = new Choice();
    if (w == 400)
     for (int i = 0, l = 25; i < 5; i++){
      chL.addItem(Integer.toString(l));  l *= 2;}
    else
     for (int i = 0, l = 20; i < 6; i++){
      chL.addItem(Integer.toString(l));  l *= 2;};
    chL.select(""+L);
    chL.addItemListener(this);
    lbL = new Label("L");  add(lbL);  add(chL);
    lbP = new Label("p");  add(lbP);
    tfP = new TextField( "" + (float)p, 5);  add(tfP);
    tfP.addKeyListener(this);
    chB = new Choice();
    chB.addItem("square  ");  chB.addItem("cylinder");  chB.addItem("torus   ");
    chB.select(periodic);
    chB.addItemListener(this);  add(chB);
  }
  public void destroy() {
    removeMouseListener(this);
  }
  public void mouseClicked(MouseEvent e){}       // event handling
  public void mousePressed(MouseEvent e) {
    painted = false;
    repaint();
    e.consume();
  }
  public void mouseReleased(MouseEvent e){}
  public void mouseEntered(MouseEvent e) {}
  public void mouseExited(MouseEvent e)  {}
  public void keyTyped(KeyEvent e){}
  public void keyPressed(KeyEvent e){}
  public void keyReleased(KeyEvent e){
    final int keyEnter = 10;
    if (e.getKeyCode() == keyEnter){
      try{ p = Double.valueOf(tfP.getText()).doubleValue();
      }catch(NumberFormatException ne){}
      painted = false;
      repaint();
    }
    e.consume();
  }
  public void itemStateChanged(ItemEvent e){
    L = Integer.parseInt(chL.getSelectedItem());
    d = w/L;  hd = w-d; L1 = L+1;
    periodic = chB.getSelectedIndex();
    painted = false;
    repaint();
  }
  
  public void paint(Graphics g) {
   if ( !painted ){
    generTime = System.currentTimeMillis();
    showStatus( "labeling clusters");
    buffGraphics.setColor(Color.white);
    buffGraphics.fillRect(0, 0, w, w);
    for (int i = 0; i < maxCl; i++) np[i] = 0;
    for (int i = 0; i < L1; i++)
     for (int j = 0; j < L; j++) cl[i][j] = -1;
    int newCl = 1, maxCl_1 = maxCl-1;
    for (int i = 1; i < L1; i++){
     int leftCl = -1;
     for (int j = 0; j < L; j++){
      if ( Math.random() > p){ leftCl = -1;  continue;}
      int downCl = cl[i-1][j];
  //System.out.println(""+i+"  "+j+"  l="+leftCl+"  d="+downCl);
      if ( downCl == -1){
       if (leftCl == -1){
        leftCl = cl[i][j] = newCl;
        if (newCl < maxCl_1) newCl++;}
       else cl[i][j] = leftCl;}
      else{
       downCl = proper(downCl);
       if (leftCl == -1){ leftCl = cl[i][j] = downCl; continue;}
       if (leftCl == downCl){ cl[i][j] = leftCl; continue;}
       if (leftCl < downCl) cl[i][j] = np[downCl] = leftCl;
       else{
        cl[i][j] = np[leftCl] = downCl;
        leftCl = downCl;}} }}
    int clA, clB, L_1 = L-1;
    if (periodic > 0){
     for (int i = 1; i < L1; i++)
      if (((clA = cl[i][0]) != -1)&&((clB = cl[i][L_1]) != -1))
       if ((clA = proper(clA)) != (clB = proper(clB)))
        if (clA > clB) np[clA] = clB;
        else np[clB] = clA;}
    int percCl = -1, topCl;
    boolean isPercolating = false;
  perc:
    for (int i = 0; i < L; i++){
     if ((percCl = cl[1][i]) == -1) continue;
     percCl = proper(percCl);
     for (int j = 0; j < L; j++){
      if ((topCl = cl[L][j]) != -1)
       if (percCl == proper(topCl)){
        isPercolating = true;
        break perc;}}}
    if (periodic > 1){
     for (int i = 0; i < L; i++)
      if (((clA = cl[1][i]) != -1)&&((clB = cl[L][i]) != -1))
       if ((clA = proper(clA)) != (clB = proper(clB)))
        if (clA > clB) np[clA] = clB;
        else np[clB] = clA;
     if ( isPercolating ) percCl = proper(percCl);}
    showStatus( "drawing");
    for (int i = 0; i < L; i++){
     for (int j = 0; j < L; j++){
      int c = cl[i+1][j];
      if ( c > 0){
       c = proper(c);
       if ( isPercolating && (c == percCl))
         buffGraphics.setColor(Color.black);
       else  buffGraphics.setColor(col[c % maxColor]);
       buffGraphics.fillRect(j*d,hd-i*d, d,d);} }}
    generTime = System.currentTimeMillis() - generTime;
    painted = true;}
   g.drawImage(buffImage, 0, hBut, this);
   showStatus( "p=" + (float)p + "  t=" + generTime + "ms");
  }
  public int proper(int label ){
    int l;
    while( (l = np[label]) != 0) label = l;
    return label;
  }
  
  public void update(Graphics g){ paint(g); }
  
  }