Added touch support, introduced in iOS 2.0 (2008), so that it works on
mobile devices and tablets. Otherwise the code is identical to the original page from 2006. It still works today, a
my awesome programming skills the Web's
backwards compatibility — add new stuff, but never break old
Puzzles 1 to 3 are warm-ups. Puzzle 4 onwards are brain-burners. Let me know if you find a difficult-to-solve puzzle!