Core Entities Cinema: cinema_id, name, address, timezone. Hall: hall_id, cinema_id, name, total_rows, total_cols, layout_type (STANDARD, IMAX, VIP). Seat: seat_id, hall_id, […]
Why DP on Strings? String DP problems have a recognizable structure: two strings of lengths m and n, where the
Requirements A gaming backend handles player authentication, matchmaking (pairing players of similar skill), real-time game state synchronization, leaderboards, and player
Core Entities Product: product_id, sku (unique stock keeping unit), name, description, category_id, unit_cost, unit_price, weight_kg, dimensions_cm (JSON), is_active. Warehouse: warehouse_id,
Backtracking Framework Backtracking = DFS + pruning. The general framework: choose a candidate for the next position, recurse, undo the
Why Multi-Region? A single-region architecture has three critical weaknesses: latency (a user in Tokyo hitting servers in us-east-1 has ~150ms
Core Entities Driver: driver_id, user_id, vehicle_id, license_number, status (OFFLINE, AVAILABLE, ON_TRIP), current_lat, current_lng, last_location_update, rating, total_trips, acceptance_rate. Vehicle: vehicle_id, driver_id,
Matrix as a Graph A 2D matrix is an implicit graph: each cell (r, c) is a node; edges connect
Requirements A media storage and delivery system stores uploaded videos or images and delivers them efficiently to users worldwide. Think
Core Entities Hotel: hotel_id, name, address, star_rating, amenities (JSON array), check_in_time, check_out_time. RoomType: type_id, hotel_id, name (STANDARD, DELUXE, SUITE, PENTHOUSE),
Trie Recap and When to Use A Trie (prefix tree) stores strings character by character. Insert and search are both
Requirements A typeahead service returns query suggestions as the user types. Google Search autocomplete, Twitter’s hashtag completion, and Stripe’s dashboard
Core Entities User: user_id, username (unique, URL-safe), email, password_hash, display_name, bio, avatar_url, role (READER, AUTHOR, EDITOR, ADMIN), created_at. Post: post_id,
Why String Algorithms? String matching and processing problems appear regularly in interviews. The naive string search (O(nm) nested loops) is
Core Requirements A file sharing platform allows users to upload, organize, and share files and folders. Key features: file upload/download,
