Low Level Design

Object-level design problems: the problem, a working Python solution, and a critique of that implementation — where it is fragile, what it costs, and what changes when the requirements grow.

• LFU cache with O(1) get, put (and delete) — a frequency list per count, and why min_freq never needs a search until you add delete.
• LRU cache with TTL and thread safety — prompt only so far.