6 min read What Is a Geo-Proximity Service? A geo-proximity service finds entities (businesses, drivers, users) near a given location. Core operations: store […] Read article
5 min read Core Entities Provider: provider_id, name, timezone, working_hours (JSONB: {“MON”: [“09:00″,”17:00”], …}), slot_duration_minutes (e.g., 30). Appointment: appointment_id, provider_id, client_id, start_time (UTC), Read article
6 min read Why Sorting Matters in Interviews Sorting is foundational: dozens of problems become O(n log n) after sorting (two-sum, 3-sum, interval Read article
6 min read Core Entities Content: content_id, type (TEXT, IMAGE, VIDEO), author_id, platform, raw_content / storage_url, created_at. ModerationDecision: decision_id, content_id, verdict (APPROVED, REMOVED, Read article
6 min read What Is Event-Driven Architecture? Event-Driven Architecture (EDA) decouples services by having them communicate through events rather than direct API calls. Read article
5 min read Matrix as a Graph A 2D matrix is an implicit graph where each cell (r, c) is a node connected Read article
5 min read Core Entities Driver: driver_id, current_location (lat/lng), status (AVAILABLE, ON_TRIP, OFFLINE), vehicle_type, rating. Rider: rider_id, payment_method_id, rating. Trip: trip_id, rider_id, driver_id, Read article
7 min read The Video Upload and Processing Problem YouTube processes 500 hours of video every minute. Each uploaded video must be transcoded Read article
7 min read Requirements Functional: send notifications via multiple channels (push, email, SMS, in-app), support notification templates with variable substitution, allow users to Read article
7 min read Requirements Functional: place orders (cart checkout → payment → fulfillment), track order status through lifecycle, handle partial fulfillment (items shipped Read article
5 min read Interval Problems: Core Insight Interval problems involve ranges [start, end]. The key operations: merge overlapping intervals, find non-overlapping sets, detect Read article
7 min read Requirements Functional: record expenses with amount, category, date, and notes; support multiple currencies with conversion; tag and categorize expenses; view Read article
7 min read Requirements Functional: 1-on-1 and group messaging, real-time message delivery, message persistence and history, read receipts (sent/delivered/read), user presence (online/offline/last seen), Read article
8 min read Requirements Functional: search available rooms by date range and city, view room details and pricing, book a room (atomic reservation), Read article
6 min read Requirements Functional: create coupons (percent off, fixed amount, free shipping), set constraints (minimum order, expiry, usage limits, specific products/categories, single Read article
