Circle Software Engineer Interview Questions
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Design banking payment scheduling system
System Design: Banking Payment System Enhancements Context You are building a minimal bank-transfer payment orchestration service (e.g., ACH/SEPA) tha...
Design in-memory DB with TTL and backup
Design a Versioned In-Memory Key → (Field → Value) Store with TTL, History, and Backup/Restore You are building an in-memory database that stores valu...
Design an in-memory KV DB with TTL, scans, backup
In-Memory Key→Hash Database: Design and Implementation Context Build a single-process, in-memory data store that supports a Redis-like hash model with...
Design payment scheduler with cancel and top-K outgoing
Design and implement an in-memory banking payment component with the following APIs: ( 1) schedulePayment(payerId, payeeId, amount, executeAt) -> paym...
Describe pair-programming challenge under time pressure
Behavioral: Pair Programming Under Ambiguity and Unfamiliar Tools Context: For a Software Engineer take-home or debrief, reflect on a real pair-progra...
Implement a simplified multi-level banking system
Implement a simplified banking system with multi-level requirements. All operations accept a stringified timestamp in milliseconds; timestamps are gua...
Design flight-price search service
System Design: Cheapest Flight Search Across Multiple Providers Context Design a backend system that searches multiple flight providers (airlines, OTA...
Trace and reduce redundant curl requests
Instrument and Optimize Client HTTP Requests for a Workflow Context You have a client that performs a defined workflow against an HTTP API (for exampl...
Implement cheapest itinerary with date filters
Implement a function that computes the cheapest itinerary from a given origin to a destination using a list of flights, where each flight has (id, sou...
Write PostgreSQL updates with date filters
Write PostgreSQL statements to: ( 1) update a flight's price and set updated_at correctly; ( 2) upsert a booking record with conflict handling; ( 3) s...