Design a URL shortener: a user submits a long URL and gets a short one, and following the short link redirects to the original.
~10 min by voice
How to approach it
This checks whether you can go through the full system design cycle on a simple problem: clarify requirements and load, choose a scheme for generating unique codes, storage and a cache for a read-heavy profile, and not forget the operational details: 301/302, analytics and abuse.
The interviewer will ask this question and listen. Think out loud and ask for a hint if you need one. When you're done, pause or tap “That's my answer”. In about a minute, your score and the points you covered show up here.