I'm one of the people who solved problems very quickly (3rd overall last year). I'm somewhat competitive by nature, and I did ACM programming challenges in undergrad (although I was never good enough to make the local team, heh). Happy to answer any questions you might have about "competitive" AoC; it's fun in a very different way than learning new languages for the competition. I personally used Python for the last few years, and I'll probably use it again this year (assuming I try to compete).

Part of it is familiarity with the format, which of course assumes they keep things reasonably similar this year. Knowing the kinds of problems that appear (parsing, graphs, optimization, reverse engineering, etc.) helped me put together a little library of code that means I'm not spending time rewriting fundamental algorithms.

Reading problem statements is one of those skills I picked up from ACM programming competitions. The problem statements usually contain a lot of fluff - to speed-code you want to be able to pluck out the relevant bits quickly so you can start formulating the solution.