6 min read DoorDash processes millions of food delivery orders daily, coordinating three parties: customers, restaurants, and drivers (Dashers). Designing a food delivery […] Read article
6 min read Robinhood democratized stock trading with zero-commission trades and a mobile-first experience for 23+ million users. Designing a stock trading platform Read article
6 min read String problems appear in 25-30% of coding interviews, making them the second most common category after arrays. String manipulation requires Read article
6 min read Google Calendar manages billions of events for hundreds of millions of users with complex scheduling requirements: recurring events with exceptions, Read article
5 min read LinkedIn connects 900+ million professionals with a rich social graph, news feed, job marketplace, and messaging system. Designing LinkedIn tests Read article
5 min read Venmo processes billions of dollars in peer-to-peer payments with a unique social feed that makes transactions visible. Designing a P2P Read article
6 min read Beyond the standard DP patterns (knapsack, LCS, linear), advanced DP techniques solve problems that seem intractable at first glance. Bitmask Read article
6 min read Beyond basic DFS traversal, advanced DFS patterns solve graph structure problems: finding cycles, identifying critical nodes and edges, and decomposing Read article
5 min read Twitter Trending Topics surfaces the most discussed subjects in real-time from billions of tweets. Designing a trending detection system tests Read article
6 min read Reddit is the “front page of the internet” with 50+ million daily active users across 100,000+ active communities (subreddits). Designing Read article
7 min read WhatsApp Status (stories) lets 2+ billion users share photos, videos, and text that disappear after 24 hours. Designing an ephemeral Read article
7 min read Google Drive serves 1+ billion users storing documents, spreadsheets, photos, and files with real-time collaboration, sharing, and cross-device sync. While Read article
7 min read Beyond basic BFS/DFS, advanced graph algorithms solve optimization problems: finding the cheapest path with constraints, detecting negative cycles, computing all-pairs Read article
7 min read Airbnb connects 4+ million hosts with 150+ million guests across 220+ countries. Designing an accommodation platform tests your understanding of Read article
7 min read System design interviews have a high failure rate — not because the problems are impossible, but because candidates make predictable Read article
