Google likes to ask lots of algorithmic questions in rapid succession. At least they did when I interviewed. Knowing of a solution or library was not good enough (they seem to reinvent their own 'everything' anyway, perhaps for good reason?). If I wanted to work there, I would practice doing classic CS problems on a whiteboard in front of friends beforehand, it's much different than real life where you can look stuff up, mull things over a cup of coffee, take a walk, etc. They were in my face the whole time.