Thanks ghj.

I was aware of top coder/leet code, though hadn't heard of code forces/at coder.

For me the adventure game give a bit more concept linkage. Take Monkey Island, I can remember how to reply to many of the sword fighting insults, or what was needed to get pieces of eight via the cannon at the circus. There's something to be said for linking problems via a memorable story, giving examples and meaning from multiple angles helps retain the content over the dryness of problem prompt/quick solve.