URL shortener

How this question breaks down

1. 1Short codesWrite path23 minTurn every long URL into a seven-character code that is unique, never reused and hard to walk, without making every write wait on one counter.
2. 2RedirectsRead path23 minAnswer 60,000 redirects a second in single-digit milliseconds by serving hot codes from memory, and pick the status code that balances speed against control.
3. 3AnalyticsRead path24 minRecord every click without slowing the redirect, then roll 1.25 billion events a day into per-link counts by hour, country, device and referrer that owners can query in milliseconds.

Work through the parts in order and you’ve covered the full design. Each part is one topic.