5 min read Backtracking Framework Backtracking = DFS + pruning. The general framework: choose a candidate for the next position, recurse, undo the […] Read article
5 min read 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, Read article
5 min read 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, Read article
5 min read Requirements A media storage and delivery system stores uploaded videos or images and delivers them efficiently to users worldwide. Think Read article
5 min read Matrix as a Graph A 2D matrix is an implicit graph: each cell (r, c) is a node; edges connect Read article
7 min read Requirements A typeahead service returns query suggestions as the user types. Google Search autocomplete, Twitter’s hashtag completion, and Stripe’s dashboard Read article
8 min read Trie Recap and When to Use A Trie (prefix tree) stores strings character by character. Insert and search are both Read article
8 min read 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), Read article
7 min read Why String Algorithms? String matching and processing problems appear regularly in interviews. The naive string search (O(nm) nested loops) is Read article
8 min read 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, Read article
8 min read Core Requirements A file sharing platform allows users to upload, organize, and share files and folders. Key features: file upload/download, Read article
7 min read Requirements and Scope An appointment scheduling system allows users (customers) to book time slots with service providers (doctors, barbers, consultants). Read article
7 min read Monotonic Stack Core Idea A monotonic stack maintains elements in a sorted order (increasing or decreasing). As new elements arrive, Read article
7 min read Core Entities Restaurant: restaurant_id, name, address, lat, lng, cuisine_type, rating, prep_time_minutes (avg), is_active, operating_hours. MenuItem: item_id, restaurant_id, name, description, price, Read article
7 min read Two-Pointer Core Idea Two pointers maintain two indices into a sorted or structured array, moving toward each other or in Read article
