Top 8 Scheduling Interview Questions
Browse 8 real-world technical and behavioral interview questions about Scheduling. Review scenarios, edge cases, and architectural best practices.
Design an elevator system for a building with N lifts. When someone presses the call button, which lift answers, and where in your code is that decided?
An elevator system splits into a state machine per lift that decides its own next floor, and a dispatcher that assigns each hall call to one lift through a pluggable strategy such as a nearest-suitable-car cost. Car buttons go straight to their lift, and one control loop owns all state, so no god class and no locks.
Users in three countries book appointments, and one of those countries has just changed when its clocks move. What do you store, and what do you refuse to store?
For a future appointment, store the local wall-clock time plus an IANA time zone ID such as Europe/Lisbon, and treat any UTC instant as a cache you recompute when time zone rules change. Refuse fixed offsets, abbreviations like IST, and server-local times. Past events are stored as UTC instants.
A DAG that finished in an hour now takes nine and blocks everything behind it. How do you find out where the time went?
Sum the task durations and compare that with the wall-clock span, because nine hours of waiting and nine hours of work are different problems. If the sum is still an hour, you are queueing on a bounded worker pool, usually behind sensors holding slots; if a task genuinely grew, its own duration history over the last thirty runs tells you whether it stepped or sloped.
How would you cut the cost of a GPU training fleet without slowing the team down?
Measure utilisation first, because most fleets pay for idle accelerators rather than for too few. Then right-size to whatever each job is bound by, move interruptible work onto spot capacity behind tested checkpointing, and pool the fleet behind one queue instead of reserving per team.
Merge a list of overlapping intervals, and justify the key you sorted by
Sorting by start time is what reduces the merge to a single scan carrying one scalar, the end of the open block; sorting by end breaks it, and sorting by end is instead correct for maximum non-overlapping selection. Both run in O(n log n), and equal timestamps decide the answer.
Field data says your page has an INP of 400 ms. How do you find the cause and fix it?
Split the interaction into input delay, processing time and presentation delay, then attribute a real interaction from the field rather than guessing. Most of the budget is usually spent before your handler runs or after it returns, so yielding and cutting rendering cost beats optimising the handler.
How do you turn an effort estimate into a delivery date you would defend, and what do you do when the sales lead has already promised an earlier one?
Convert effort to duration through explicit productive capacity, then check it against the critical path and the customer's dependencies, because dates are often bound by sequence rather than effort. Against a promised date, commit a smaller scope rather than a compressed plan.
What actually happens during a context switch, and why should an application developer care?
A context switch in an operating system saves one thread's CPU state, runs the scheduler and restores another thread. Application developers care because excessive switches add latency through cache and TLB disruption, lock contention and oversized thread pools. It also connects scheduling to the point an interviewer is testing.