The interviewing process included two online pair-coding rounds of similar complexity. Both rounds were easier than 99.9% of interviews I had before, and all their problems could be solved by any high school student. Surprisingly, I received a rejection email with phrases like "interviewer was not satisfied with your solutions" or something similar. This sounded ridiculous because, for the last 15 minutes of the interview, after three or four correctly answered follow-up questions, the interviewer didn't know what else to ask and tried to come up with new questions on the fly.

My email asking for the reasons for rejection was, of course, ignored.

The easiest 'stack' and 'map' problems you are able to come up with.