I don't remember anything except the in-person part anymore.

All I remember that the in-person part exhaustively involves permutations and backtracking. Practice that kind of problem.

And then there was a section of just talking about what you've worked on and why you made the design choices you did, what kind of problems you ran into and how you solved them, etc, the usual.

Having consequently accepted an offer, I am sorry to say the nature of the work here is quite distantly unrelated to their interview content. They may as well be hiring sushi chefs based on their ability to repair cars.

While the interview focuses on intense algorithmic application, the actual job mostly involves copy/pasting from an enormous monolith of pre-written legacy Perl code.

Permutations and backtracking.