The next step is to implement undo.
Robot University -- a 2D DirectX Puzzle
As for my Android textbook study goes, I finished typing in Ed Burnetts's Sudoku example, and the program seems to more or less run, but I still struggle to understand how the program really works. So I decided to take a detour and start writing my own game program. In this method, I will be refering back to the textbook each time I come across a question. Doing it this way, I will probably digest the textbook concepts better.
I'm currently writing web-based hint pages. I wonder if users will hesitate to press a button that will launch a default browser and jump to a hint page on my web site because of security concerns. Of course, I will never transmit any personal information from the user's PC to my web site. Does anybody have an opinion?