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Design an Elevator Control System is a medium low-level design interview question covering low level design, object oriented design, state machine, design patterns, class design — the kind asked at FAANG (Facebook/Meta, Apple, Amazon, Netflix, Google) and AI-first companies like Anthropic, OpenAI, and Nvidia.
Design the controller for a bank of 4 elevators serving 20 floors in one building. Floors have up and down buttons; each car has a button per floor. The system should minimise average wait time, but no request may be ignored indefinitely. Model the cars, the requests, and the dispatch policy. There is a fire recall mode that sends every car to the ground floor, and cars can be taken out of service individually.
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