cache

The single most-asked design-a-data-structure question in FDE loops. There's an interview-legal Python shortcut and a from-scratch version, and knowing when to offer which is half the grade.

Anthropic's reported twist on the LRU staple: the cache is a decorator, the keys are arbitrary call signatures, and the follow-up writes it to disk. The kwargs-ordering and unhashable-argument traps are the whole interview.