Well leetcode asks you to implement the data structure, not how and when to use which data structure. I don’t need to know how to implement a bloom filter on a whiteboard off the top of my head to know when to use it.

Hell, the number of times I've used a lot of the data structures that come up in leetcode exercises without at least looking at some reference material is pretty small. I usually assume I'm going to misremember it, and go double check before I write it so I don't waste ages debugging later.