Problems

Design a ride-sharing platform like Uber that allows riders to request rides and get matched with nearby drivers in real-time. The platform should support: - User registration and authentication (riders & drivers) - Real-time driver/rider matching based on proximity - Live GPS location tracking during rides - Surge pricing during high-demand periods - Payment processing (credit cards, wallets) - Ride history and receipts - Driver ratings and reviews - Push notifications for ride updates Scale target: 50 million monthly active users, 10 million rides per day, operating across 60+ countries.

Design the core timeline and tweet service for a social media platform like Twitter/X. The platform should support: - Posting tweets (text, images, videos up to 280 chars text) - Home timeline (fan-out on read vs fan-out on write for feed generation) - Following/followers relationship management - Retweets, likes, and replies - Real-time timeline updates for new tweets - Hashtag trending topics (computed in real-time) - User search and tweet search (full-text) - Push notifications for mentions and interactions - Media upload and CDN delivery - Tweet thread support Scale target: 400 million monthly active users, 500 million tweets per day, average user follows 200 accounts, celebrity accounts may have 50M+ followers.

Design a web application similar to ChatGPT that allows users to have multi-turn conversations with large language models. The platform should support: - User authentication and session management - Multi-turn conversation threads with context retention - Real-time streaming of LLM responses (token by token) - Conversation history with search and organization - Multiple model selection (different LLM backends) - Rate limiting and usage quotas per user/tier - Markdown rendering in responses (code blocks, tables, etc.) - File upload and multimodal input (images, documents) - Sharing conversations via public links - Admin dashboard for monitoring usage and costs Scale target: 20 million daily active users, 500 million messages per day, average conversation length of 10 turns.