Design & Math

These are the "implement this" problems. Meta hands you a class signature or a function and a complexity target, then watches you build the machine behind it. Three of them recur enough to drill on their own: a weighted a Premium question, raising a number to a power, and a least-recently-used cache. Each hides a single trick, and once you see it the code is short.

The tricks don't overlap, which is part of why Meta likes the set. A prefix-sum array turns "pick by weight" into a lookup. Halving the exponent turns a million multiplications into twenty, and a linked list bolted onto a hash map answers in constant time. Learn the move and the problem follows.