It's not really your fault, but defeating Google-gotcha interview questions is a very distorting motivation. I'd like to think that this material is worth studying because it will help you to achieve things you otherwise could not, whether at Google or elsewhere.
But that leads to a different kind of study: deep dives into specialized subjects relevant for the task at hand, rather than attempting to maintain shallow coverage over a broad field.
If they specifically asked for "powerset" that might be considered a gotcha question, but a powerset is another way of thinking of binary enumeration[0], which isn't that rare.
[0] by that I mean both the case of counting in binary, as well as enumerating all the ways you can have or not have some things--you might care about that when considering all the interactions of config flags you might have to deal with.
this is exactly the case. had i just remember what a power set was instead of say something dumb like "all the n-k combination of these children something someting" it would have gone much better.
But that leads to a different kind of study: deep dives into specialized subjects relevant for the task at hand, rather than attempting to maintain shallow coverage over a broad field.