Coupon and Discount System Low-Level Design
6 min read Requirements Create and manage discount coupons (percentage, fixed amount, free shipping) Apply coupon to a cart: validate, compute discount, prevent […] Read article
System Design
System Design
Permission and Authorization System Low-Level Design
6 min read Permission Models Overview Three main models: ACL (Access Control List): per-resource list of who can do what. Simple, fine-grained, but Read article
Algorithms, Coding Interview Questions
Two Pointers Advanced Interview Patterns
6 min read When to Use Two Pointers Two pointers reduce O(n²) brute force to O(n) or O(n log n) by exploiting sorted Read article
System Design
Hotel Reservation System Low-Level Design
6 min read Requirements Search available rooms for a date range (check-in, check-out, guests, room type) Book a room: prevent double-booking the same Read article
System Design
Distributed Configuration Service Low-Level Design
6 min read What is a Distributed Configuration Service? A configuration service manages application settings, feature flags, and operational parameters across a distributed Read article
Algorithms, Coding Interview Questions
Bit Manipulation Interview Patterns
6 min read Essential Bit Operations x & y # AND: both bits must be 1 x | y # OR: at least Read article
System Design
Task Queue System Low-Level Design
6 min read Requirements Producers enqueue tasks; workers process them asynchronously At-least-once delivery: tasks must not be lost on worker crash Retry with Read article
System Design
A/B Testing Platform Low-Level Design
6 min read What is A/B Testing? A/B testing (controlled experimentation) randomly assigns users to experimental variants and measures which variant produces better Read article
Algorithms, Coding Interview Questions, Graphs
Topological Sort Interview Patterns
6 min read What is Topological Sort? A topological ordering of a directed acyclic graph (DAG) is a linear ordering of vertices such Read article
System Design
Fraud Detection System Low-Level Design
6 min read Requirements Detect fraudulent transactions in real time (<200ms per transaction decision) Flag suspicious user behavior: account takeover, card testing, synthetic Read article
System Design
Real-Time Analytics Platform Low-Level Design
6 min read Requirements Ingest billions of events per day (page views, clicks, transactions, errors) Support real-time dashboards with <10 second lag Support Read article
Algorithms, Coding Interview Questions
Stack Interview Patterns
6 min read Core Idea A stack (LIFO) is the right tool when the most recently seen element determines the action for the Read article
System Design
Ad Click Tracker System Low-Level Design
6 min read Requirements Record every ad click event (ad_id, user_id, timestamp, ip, device_type) Query click counts per ad for any time range Read article
System Design
API Gateway Low-Level Design
6 min read What an API Gateway Does An API gateway is the single entry point for all client requests to a microservices Read article
System Design
Game Leaderboard System Low-Level Design
5 min read Requirements Update a player score in real time Query the global top-100 leaderboard Query a player’s exact rank among all Read article