Machine Coding Round interview questions

Machine coding round questions such as parking lot, rate limiter, Splitwise, elevator, vending machine, and other timed build-it problems.

3 questions in Low-Level Design & OOD.

Low-Level Design & Object-Oriented DesignA 23-minute read on how the topic fits together, before the questions.Low-level design fundamentals60 short answers on one page, for revising rather than studying.

medium2

mediumCodingDesign

Design a rate limiter that allows N requests per client per minute. Write the class.

A rate limiter machine coding solution should reject fixed-window boundary bursts, usually with a token bucket. It needs no per-request history and stores two numbers per client, but only if refill is computed lazily from a timestamp rather than by running a background thread. Use this rate limiting answer to show the decision, trade-off, and evidence rather than a memorised definition.

4 minmid, senior

mediumCodingDesign

Build a shared-expense tracker. Three people split a bill of ten pounds evenly - write the classes, and tell me where the missing penny goes.

A Splitwise-style machine coding answer turns on one invariant: the shares of an expense must sum to the expense total exactly, in every currency, forever. That forces money into integer minor units and forces a stated rule for allocating the remainder.

6 minmid, senior, staff

hard1

hardDesignCoding

Design a parking lot system — you have 90 minutes, working code at the end.

In a parking lot machine coding round, scope one deterministic flow of park, unpark and charge, model Vehicle, Slot, Level, Ticket and a ParkingLot facade, then push slot allocation and pricing behind strategy interfaces so review-time variants are configuration rather than surgery.

6 minmid, senior, staff