You can get into bucket 2 if you just use hash tables and know the most basic information about their use. Plenty of candidates were in this bucket and passed the rest of the interview.

I still gave the rest of the non-hash table interview to every candidate. What I'm saying what the hash table question was a tremendous predictor of candidate success in every other aspect of the interview. System design, algorithms, problem solving, etc.

Candidates that didn't know anything about a hash table, even just the most basic idea of "fast insert/lookup/delete key-value datastructure", almost universally failed almost every aspect of the rest of the interview.

Candidates that know the basics could go either way.

Candidates that know all the details almost universally crushed every other aspect, including very unrelated things like distributed system design.

For people with recent experience building hash tables. What sticks over the years is how you work with them and where they are a good solution to a problem. The more experience you have in using them, the less likely you are to remember how to build them, because that information was never used and got pushed out of memory by all of the other things an experienced developer needs to remember.

Not even that.

There are people out there who have built hash tables, who don't even know what they've built is called a hash table by educated folks. I know this, because I formerly happened to have worked with such a guy, after needing to change some of his code and discussing it with him.

They did say "low level programming backend job". At least a large subset of what they mentioned should be common knowledge then.