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
System Design
System Design
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
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
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
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
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
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
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
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
System Design
Messaging System (Chat) Low-Level Design
6 min read Requirements One-on-one messaging and group chats (up to 500 members) Real-time message delivery (< 100ms), offline message storage, read receipts Read article
Algorithms, Coding Interview Questions, Math
Number Theory Interview Patterns
6 min read GCD and LCM Euclidean algorithm: gcd(a,b) = gcd(b, a%b), base case gcd(a,0) = a. Time O(log min(a,b)). LCM: lcm(a,b) = Read article
System Design
Event Ticketing System Low-Level Design
6 min read Requirements Users can browse events, select seats from a seat map, reserve seats, and complete payment Prevent double-booking: no two Read article
System Design
Video Streaming Platform (YouTube/Netflix) Low-Level Design
6 min read Upload Pipeline Raw video upload → object storage (S3 raw bucket) → message published to transcoding queue (SQS/Kafka) → transcoding Read article
Algorithms, Coding Interview Questions
Prefix Sum Interview Patterns
5 min read Core Idea Build a prefix array where prefix[i] = arr[0] + arr[1] + … + arr[i-1]. Then any range sum Read article
System Design
Social Graph System Low-Level Design
7 min read Two Graph Models The first design decision is the relationship model: Directed graph (Twitter/Instagram follow): A follows B does not Read article
