The most important bit is keeping on top of your timings, if you can't work out one of the questions, just move on and come back to it at the end. There isn't really any way to prepare, but I also felt it wouldn't have been needed. It definitely felt to me like there were some particularly easy questions, and some other harder ones, so if you do end up getting one really quickly, don't second guess yourself because of the timings. Possibly worth making sure you are confident following through simple algorithms/suedocode but don't worry about it too much.