Start by agreeing on the problem and its limits. Sketch a design you can explain, then use the remaining time to discuss the parts that need closer attention. Treat the timing below as a practice plan rather than a rule for every interview.
A Practice Schedule
0 to 5 minutes: scope and constraints. 5 to 15 minutes: high level design. 15 to 30 minutes: deep dives. 30 to 40 minutes: bottlenecks and scaling. 40 to 45 minutes: tradeoffs and recap.
Explain Your Choices
Explain why you made each important choice. Ask when a requirement is unclear and describe what you would change if the traffic, budget or reliability needs were different.
