For most software engineering jobs, the implementation of tries and whatnot is completely divorced from the actual day-to-day work, work that's generally on a much higher level of abstraction to the interview questions. It's the equivalent of interviewing a chemist based on his knowledge of physics.

If you're a Google or HFT firm working on massive scale or optimizing super low latency systems, sure it very well may be critical knowledge. If you're some random company with a CRUD app, this kind of hiring process isn't going to optimize for the most qualified candidates for the job.