Build Spotify's Song Radio Feature Premium
Design a real-time playlist generator that uses a seed song to produce an infinite radio stream of acoustically and contextually similar tracks, personalizes the mix per listener, and avoids repetition across sessions.
Build a Time-Series Metrics Store Premium
Design a metrics storage engine that compresses billions of data points efficiently, supports fast range queries for dashboard rendering, and retains high-resolution data for 15 days before downsampling.
Build Twitter's At-Mention Fan-Out for Celebrities Premium
Design a fan-out system that notifies the followers of a celebrity with 100 million followers when they are mentioned, without triggering a write storm that takes down the database.
Build Twitter's Trending Topics Pipeline Premium
Design a system that detects emerging viral signals from a stream of 500,000 tweets per second, computes trending topics per region, and refreshes trends every 60 seconds without reprocessing the full history.
Build Uber's Real-Time Driver-Rider Matching System Free
Design a matching system that pairs riders with the nearest available driver in dense urban areas within 2 seconds, handles thousands of concurrent match requests, and degrades gracefully during demand spikes.
Build Uber's Surge Pricing Engine Free
Design a dynamic pricing system that detects supply-demand imbalance in each geographic zone, computes surge multipliers in under a second, and communicates price changes to riders and drivers without race conditions.
Build TinyURL - A URL Shortener at Scale Premium
Design a URL shortening service that generates collision-free short codes, handles 100,000 redirects per second with sub-10ms latency, and tracks click analytics without slowing down redirects.
Build a Vector Search Engine Premium
Design an approximate nearest neighbor search service that indexes 100 million high-dimensional embeddings, answers similarity queries in under 20ms, and supports live index updates without downtime.
Build a WebSocket-Based Presence System Premium
Design an online presence and typing indicator system that tracks 10 million concurrent users, propagates status changes to relevant subscribers in under 200ms, and handles connection drops gracefully.
Build YouTube's View Count System Premium
Design a view counting system that accurately tracks billions of views per day, shows counts that update in near real-time on video pages, and resists inflation from bots and refreshes without blocking the video serve path.