Meeting Room Scheduler · Analysis

01 · Frame the problem

Understand the central challenge

Design a room scheduling library for one-time meetings. Rooms have capacity and equipment requirements. Concurrent requests may select overlapping times, and editing a meeting must not lose its original reservation on failure.

Scheduling correctness depends on interval semantics and shared overlap enforcement. Time-zone interpretation must be resolved before comparing instants, and failed rescheduling must preserve the existing reservation.

02 · Find the design pressure

Start simple, then identify the gap

Begin with half-open intervals and room-scoped ownership. A controller-side availability check races another booking. Enforce overlap prevention in the repository transaction, with version guards for reschedule/cancel and a clear adjacent-booking rule.

Model room reservations as half-open intervals of explicit instants. Enforce overlap prevention in the durable repository and make creation, rescheduling and cancellation idempotent or version guarded. Validate start < end, attendees and required equipment. Convert unambiguous timezone inputs to instants; this exercise handles one-time reservations, not recurrence expansion. AvailabilityPolicy filters eligible rooms. A shared transactional repository serializes per-room booking or uses an overlap exclusion constraint before inserting an active reservation. A reschedule checks the expected reservation version and validates the replacement interval in one transaction. On conflict or stale version it leaves the prior reservation intact. Cancellation marks a reservation inactive once and increments its version. Idempotency keys return matching previous create results and reject different payloads with the same key.

03 · Define success

Requirements to preserve

Use a consistent half-open interval model for reservations.
Atomically reject overlapping active reservations for a room.
Filter by room capacity and required equipment.
Support idempotent create, guarded reschedule and cancellation.

04 · Identify the correctness boundary

Invariants, representation and mutation boundaries

Normalize user times into explicit instants and retain the originating time-zone policy where needed. Half-open intervals permit adjacent reservations. Overlap prevention belongs in the shared repository transaction, and rescheduling validates a staged replacement before releasing the current reservation.

05 · Make it concrete

Reason through a worked example

Booking [10:00,11:00) and [11:00,12:00) can share a room. A request for [10:30,11:30) conflicts. If rescheduling the first booking into an occupied period fails, its original interval remains booked. Concurrent creates cannot both pass an unprotected check-then-insert overlap test.