I'm a CS guy who was completely forgotten red-black trees after about 5 years in the real world. I've also forgotten how to do flux integrals. I could pick both up if required. This is an example, IMHO, about why technical questions on interviews can be misleading. If they can honestly explain they'd have to look something up, that's *totally* fine. You want people that can learn quickly and do good work (including work that involves making up *new* things), not just folks that are walking textbooks. Red-black trees? I probably forgot that a week after the datastructures final.