Well, it happened. When applying for a job, I got sent to a Codility test. And even though I already had some good practice with them, I managed to do badly in stupid ways – ways that 2 years ago I had already identified and even taken notes on. Just, in the heat of the moment I forgot about those rules of thumb. And in fact I think these hints should be given by Codility themselves – because otherwise you are practically ambushed, even more so if you didn't take the time to thoroughly explore how they work. So here are my hints-to-self, now for everyone. The summary is: don't think of Codility as a coding interview; this is primarily about getting something (anything!) working, ASAP.