System design interview question
"Design a URL shortener. A user submits a long URL and gets back a short one; anyone visiting the short URL is redirected. 100 million new links a day, 10 billion redirects a day. Tell me how the short code is generated."
The classic screening question, chosen because it is small enough to finish and has exactly one non-obvious decision: how to generate short codes that are unique, short, and non-guessable without coordination overhead. The secondary content is the enormous read:write asymmetry and why that makes it a caching problem.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
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