String Hashing Interview Patterns
Why String Hashing? Naive string comparison is O(L) per comparison where L is the string length. String hashing converts a […]
Algorithms, Coding Interview Questions, String
Design, System Design
Distributed Configuration Service Low-Level Design
What is a Distributed Configuration Service? A configuration service manages application settings, feature flags, and operational parameters across a distributed
Design, System Design
Hotel Reservation System Low-Level Design
Requirements Search available rooms for a date range (check-in, check-out, guests, room type) Book a room: prevent double-booking the same
Algorithms, Coding Interview Questions
Two Pointers Advanced Interview Patterns
When to Use Two Pointers Two pointers reduce O(n²) brute force to O(n) or O(n log n) by exploiting sorted
Design, System Design
A/B Testing Platform Low-Level Design
What is A/B Testing? A/B testing (controlled experimentation) randomly assigns users to experimental variants and measures which variant produces better
Design, System Design
Task Queue System Low-Level Design
Requirements Producers enqueue tasks; workers process them asynchronously At-least-once delivery: tasks must not be lost on worker crash Retry with
Algorithms, Coding Interview Questions
Bit Manipulation Interview Patterns
Essential Bit Operations x & y # AND: both bits must be 1 x | y # OR: at least
Design, System Design
Real-Time Analytics Platform Low-Level Design
Requirements Ingest billions of events per day (page views, clicks, transactions, errors) Support real-time dashboards with <10 second lag Support
Design, System Design
Fraud Detection System Low-Level Design
Requirements Detect fraudulent transactions in real time (<200ms per transaction decision) Flag suspicious user behavior: account takeover, card testing, synthetic
Algorithms, Coding Interview Questions, Graphs
Topological Sort Interview Patterns
What is Topological Sort? A topological ordering of a directed acyclic graph (DAG) is a linear ordering of vertices such
Design, System Design
API Gateway Low-Level Design
What an API Gateway Does An API gateway is the single entry point for all client requests to a microservices
Design, System Design
Ad Click Tracker System Low-Level Design
Requirements Record every ad click event (ad_id, user_id, timestamp, ip, device_type) Query click counts per ad for any time range
Algorithms, Coding Interview Questions
Stack Interview Patterns
Core Idea A stack (LIFO) is the right tool when the most recently seen element determines the action for the
Design, System Design
Distributed Lock System Low-Level Design
Why Distributed Locks? In a distributed system, multiple servers run the same code concurrently. A distributed lock ensures only one
Design, System Design
Game Leaderboard System Low-Level Design
Requirements Update a player score in real time Query the global top-100 leaderboard Query a player’s exact rank among all