Hanoi Tower

The backend algorithm is just a few lines big..., it's all about rendering.
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The core code is pretty cool:

 public class BackendAlgorithm
 {
   public static void move(int n, String from, String to, String using)
   {
     if (n == 0)
       return;
     move(n-1, from, using, to);
     HanoiContext.getInstance().fireMoveRequired(from, to); // Broadcast the move
     move(n-1, using, to, from);
   }
 }

Again, it's mostly about rendering... 99% of the code of the applet above is for the graphical display!
The simplest user interface would look like this:

 package hanoitower;
 
 public class BackendAlgorithm
 {
   public static void move(int n, String from, String to, String using)
   {
     if (n == 0)
       return;
     move(n-1, from, using, to);
     System.out.println("Moving from " + from + " to " + to);
     move(n-1, using, to, from); 
   }
  
   public static void main(String[] args) throws Exception
   {
     move(Integer.parseInt(args[0]), "A", "C", "B"); // Moving A to C using B
   }
 }

Run it this way:

 Prompt> java hanoitower.BackendAlgorithm 4
 Moving from A to B
 Moving from A to C
 Moving from B to C
 Moving from A to B
 Moving from C to A
 Moving from C to B
 Moving from A to B
 Moving from A to C
 Moving from B to C
 Moving from B to A
 Moving from C to A
 Moving from B to C
 Moving from A to B
 Moving from A to C
 Moving from B to C

Boom!