#state machines

8 state machines interview questions, asked at Stripe, Amazon, Meta and 1 more company. Last asked Oct 2026.

Split-tender payments with gift cards, surcharges and refundsCodingAt a retail point of sale one purchase can be paid with several methods, for example part on a gift card and the rest on a credit card (a split-tender transaction). Write the code…
Last asked Oct 2026
Financial account ledger with acceptance, limits and settlementCodingImplement processledger(commands), which handles commands in order: set up accounts, request deposits and query balances. Return the query answers as one comma-separated string…
Last asked Sep 2026
Payment command parser and state machineCodingBuild the parser and the object-oriented state machine behind a payment command interface. Every command line has the same fixed number of positions, with empty strings in the…
Last asked Aug 2026
Valid numberCodingReturn whether a string is a valid number: an integer or decimal with an optional sign, optionally followed by an exponent (e or E and an integer). Spell out the rules first, then…
Last asked Apr 2026
Sticky load balancer for long-lived connectionsCodingSimulate a load balancer that routes long-lived WebSocket connections to several Jupyter servers. Process a sequence of requests such as CONNECT, DISCONNECT and SHUTDOWN: place…
Last asked Feb 2026
Robot charging controller with exclusive stationsCodingA fleet of robots shares a small number of charging stations. A robot whose battery drops below 50% should go to a free station, and a robot charging above 95% may leave and go…
Last asked Jan 2026
Load balancer with worker states, a priority queue and autoscalingCodingIn a time-boxed backend round, write a small load balancer in Python. Workers move through states (for example starting, idle, busy, draining), requests go to workers through a…
Last asked Dec 2025
Memory usage switcher with configurable thresholdsOO designDesign and code an in-memory switcher that watches memory usage and switches between states (or targets) when usage crosses thresholds the caller can configure. Cover how…
Last asked Sep 2025