I try to optimize the code as much as I reasonably can without slowing me down, you can think of it as "-O1.5" on a C compiler. I try to find algorythmically fast solutions (like binary search on day 1) but I'm not that great at it. (I'm going to uni for computer science next fall!)
Over time I figure out better and more efficient ways to do things, but those fixes don't get backported! Which means the early days' code quality might be (significantly) lower than the later ones.