Exactly. When I was doing this, one of the questions required the use of a custom comparator. I spent the remaining 20 minutes of the challenge trying (and failing) to remember the correct syntax for writing a comparator until it timed out.
I also did that question. You had access to the full Java docs.
I left a nice note explaining how I spent a lot of time trying to do it with the language feature, but couldn't due to runtime restrictions, and gave them a working non-optimized solution.
I was emailed to schedule an interview the next day.
