I spent way too long on the design half and then rushed the estimation, which I think was the wrong call.
Start by clarifying requirements and constraints, then break the problem into user needs, system components, and capacity estimation. Use a structured framework to design the elevator system and estimate the number of elevators based on peak demand and service level targets.
Pro tip: Always state your assumptions explicitly and validate them with the interviewer; this shows you can navigate ambiguity and collaborate effectively. Also, consider both quantitative (e.g., waiting time) and qualitative (e.g., user experience) factors in your design.
Ask questions to understand building specifics (height, floors, population), user expectations (wait time, capacity), and any constraints (budget, space, technology).
Identify key user groups (employees, visitors) and their patterns (peak hours, traffic flow). Set service level targets such as average wait time and maximum wait time.
Outline the elevator system architecture: number of shafts, elevator types (passenger, freight), control algorithms (smart grouping, destination dispatch), and safety features.
Calculate peak demand using building population, arrival rates, and elevator capacity. Use formulas or simulation to determine the number of elevators needed to meet service level targets.
Check if the design meets requirements, consider trade-offs (cost vs. performance), and propose optimizations or alternatives (e.g., double-deck elevators, sky lobbies).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.