Saidel - I've just sent you an email with the source. I would upload it here but it's done on an old version of Greenfoot so not sure it would still work correctly. Feel free to have a play around though!

A note on the performance side of things - if you're trying to go faster than the built in library classes, I can near guarantee that however much work you put in you won't manage it! There's many reasons for this, from the sheer amount of manpower put in, to the close links the guys writing the library code have with the ones implementing the VM, to (as mentioned) the fact that on all common platforms the AWT graphics class will use some form of hardware acceleration. That's not to say this scenario is worthless at all - demonstrating algorithms and how they work is a nice idea for a scenario in all manner of cases. Just don't get too hung up on trying to drive to be the fastest :-)

I know it's not yet finished, but one thing that would be good to implement is if you click on a blank, all the other blanks in that section are filled in. :-)