Each problem walks the seven stages of a real interview and ends with the trade-offs an interviewer will push on. Study the reference, then run a timed practice.
Run Practice first without reading the reference. Score yourself with the rubric, then read the reference and note what you missed. Repeat a week later.
Turn long URLs into short, unique aliases and redirect users at very high read volume. A classic warm-up that tests key generation, read-heavy caching and analytics.
Limit requests per client across a fleet of API servers with low latency and predictable behaviour under failure.
Users post short messages and follow others; generate a home timeline that is fast to read and tolerates celebrity accounts.
One-to-one and group messaging with delivery receipts, offline support and message ordering.
Send push, SMS and email notifications from many internal services reliably, with priorities, rate limits and user preferences.
Design a horizontally scalable in-memory cache with partitioning, replication and eviction.
Track driver locations in real time and match riders with nearby drivers within seconds.
Upload, transcode and stream video globally with adaptive bitrate and low start-up latency.