Divide and Conquer Interview Patterns
The Pattern Divide and conquer splits a problem into independent subproblems, solves each recursively, and combines the results. Three steps: […]
Algorithms, Coding Interview Questions
Design, System Design
Messaging System (Chat) Low-Level Design
Requirements One-on-one messaging and group chats (up to 500 members) Real-time message delivery (< 100ms), offline message storage, read receipts
Algorithms, Coding Interview Questions, Math
Number Theory Interview Patterns
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) =
Design, System Design
Event Ticketing System Low-Level Design
Requirements Users can browse events, select seats from a seat map, reserve seats, and complete payment Prevent double-booking: no two
Design, System Design
Video Streaming Platform (YouTube/Netflix) Low-Level Design
Upload Pipeline Raw video upload → object storage (S3 raw bucket) → message published to transcoding queue (SQS/Kafka) → transcoding
Algorithms, Coding Interview Questions
Prefix Sum Interview Patterns
Core Idea Build a prefix array where prefix[i] = arr[0] + arr[1] + … + arr[i-1]. Then any range sum
Design, System Design
Content Delivery Network (CDN) Low-Level Design
What a CDN Does A Content Delivery Network caches content at edge Points of Presence (PoPs) geographically close to users,
Design, System Design
Social Graph System Low-Level Design
Two Graph Models The first design decision is the relationship model: Directed graph (Twitter/Instagram follow): A follows B does not
Design, System Design
Ride-Sharing App (Uber/Lyft) High-Level System Design
Core Services A ride-sharing platform like Uber or Lyft decomposes into focused microservices: Location Service: ingests driver GPS pings, maintains
Design, System Design
File Storage System (Google Drive / Dropbox) Low-Level Design
Requirements Design a file storage system like Google Drive or Dropbox supporting: Upload and download files up to 50 GB
Algorithms, Coding Interview Questions, Design
Object-Oriented Design Patterns for Coding Interviews
Design patterns appear in coding interviews in two ways: the interviewer asks you to implement a specific pattern, or you’re
Design, System Design
E-Commerce Platform Low-Level Design
An e-commerce platform touches nearly every backend concept that appears in system design interviews: relational data modeling, inventory consistency, distributed
Design, System Design
Typeahead Search (Autocomplete) System Low-Level Design
Typeahead search (also called autocomplete) is one of the most latency-sensitive features in a modern product. Users expect suggestions to
Design, System Design
Ticket Booking System Low-Level Design
A ticket booking system like Ticketmaster must handle concurrent seat selection, hold expiry, payment confirmation, and flash sale traffic spikes.
Design, System Design
Proximity Service (Find Nearby) Low-Level Design
A proximity service answers “find all restaurants / drivers / users within R km of this location” with low latency