7 min read Core Responsibilities An identity service (also called an IAM or auth service) handles: Authentication (who are you?) — verifying credentials […] Read article
7 min read Union-Find Core Concept Union-Find (Disjoint Set Union, DSU) efficiently tracks which elements belong to the same connected component. Two operations: Read article
7 min read Core Entities PaymentIntent: intent_id (UUID), merchant_id, customer_id, amount (integer cents), currency, status (CREATED, PROCESSING, REQUIRES_ACTION, SUCCEEDED, FAILED, CANCELLED, REFUNDED), payment_method_id, Read article
7 min read Core Architecture A search system takes a text query and returns a ranked list of documents (web pages, products, articles). Read article
7 min read Sliding Window Core Idea Sliding window maintains a window [left, right] over a linear data structure (array, string). As the Read article
7 min read Core Entities User: user_id, email, timezone, working_hours (JSON: {mon: “9:00-17:00”, …}). Calendar: calendar_id, user_id, name, color, is_primary, visibility (PRIVATE, PUBLIC, Read article
7 min read What is a Document Store? A document store (MongoDB, DynamoDB, Couchbase, Firestore) stores JSON-like documents with flexible schemas — each Read article
6 min read When Does Greedy Work? Greedy works when the locally optimal choice at each step leads to a globally optimal solution. Read article
7 min read Core Requirements A collaborative document editor allows multiple users to edit the same document simultaneously, with changes reflected in near-real-time Read article
7 min read Requirements and Scale An analytics pipeline collects events from product surfaces (web, mobile, backend services), processes them in real time Read article
7 min read DP on Trees Overview Tree DP solves optimization problems where the answer for each node depends on the answers for Read article
7 min read Core Entities Event: event_id, name, venue_id, event_date, doors_open, start_time, status (ON_SALE, SOLD_OUT, CANCELLED, COMPLETED), total_capacity. Venue: venue_id, name, address, seating_map_url, Read article
6 min read The Four Traversals Binary tree traversals: Inorder (left, root, right) — gives sorted order for a BST. Preorder (root, left, Read article
7 min read Core Entities Cart: cart_id, user_id (nullable for guest), session_id (for guest carts), status (ACTIVE, MERGED, ORDERED), created_at, updated_at, expires_at. CartItem: Read article
6 min read Core Requirements A coupon system allows businesses to issue discount codes that customers apply at checkout. Types: percentage discount (20% Read article
