Matrix and Graph Interview Patterns: Island Counting, Shortest Path, and Cycle Detection (2025)
5 min read Matrix as a Graph A 2D matrix is an implicit graph: each cell (r, c) is a node; edges connect […] Read article
Algorithms
System Design
System Design: Typeahead / Search Autocomplete — Trie Service, Ranking, and Low-Latency Delivery
7 min read Requirements A typeahead service returns query suggestions as the user types. Google Search autocomplete, Twitter’s hashtag completion, and Stripe’s dashboard Read article
Algorithms
Advanced Trie Interview Patterns: Word Search, Palindrome Pairs, and Replace Words (2025)
8 min read Trie Recap and When to Use A Trie (prefix tree) stores strings character by character. Insert and search are both Read article
System Design
Low-Level Design: Hotel Management System — Room Booking, Check-In, and Billing
8 min read Core Entities Hotel: hotel_id, name, address, star_rating, amenities (JSON array), check_in_time, check_out_time. RoomType: type_id, hotel_id, name (STANDARD, DELUXE, SUITE, PENTHOUSE), Read article
Algorithms
String Algorithm Interview Patterns: KMP, Rabin-Karp, Z-Function, and Trie Applications (2025)
7 min read Why String Algorithms? String matching and processing problems appear regularly in interviews. The naive string search (O(nm) nested loops) is Read article
System Design
Low-Level Design: Blog Platform — Content Management, Comments, and SEO-Friendly URLs
8 min read Core Entities User: user_id, username (unique, URL-safe), email, password_hash, display_name, bio, avatar_url, role (READER, AUTHOR, EDITOR, ADMIN), created_at. Post: post_id, Read article
System Design
System Design: File Sharing Platform (Google Drive/Dropbox) — Storage, Sync, and Permissions
8 min read Core Requirements A file sharing platform allows users to upload, organize, and share files and folders. Key features: file upload/download, Read article
System Design
System Design: Appointment Scheduling — Time Slot Management, Booking Conflicts, and Reminders
7 min read Requirements and Scope An appointment scheduling system allows users (customers) to book time slots with service providers (doctors, barbers, consultants). Read article
Algorithms
Monotonic Stack Interview Patterns: Next Greater Element, Largest Rectangle, and Stock Span (2025)
7 min read Monotonic Stack Core Idea A monotonic stack maintains elements in a sorted order (increasing or decreasing). As new elements arrive, Read article
System Design
Low-Level Design: Online Food Delivery (DoorDash/Uber Eats) — Order Lifecycle, Driver Assignment, and ETA
7 min read Core Entities Restaurant: restaurant_id, name, address, lat, lng, cuisine_type, rating, prep_time_minutes (avg), is_active, operating_hours. MenuItem: item_id, restaurant_id, name, description, price, Read article
System Design
System Design: Live Comments — Real-Time Delivery, Moderation, and Spam Prevention at Scale
6 min read Requirements A live comments system allows users to post comments on content (articles, videos, livestreams) and see other users’ comments Read article
Algorithms
Advanced Two-Pointer Interview Patterns: Three Sum, Trapping Rain Water, and Container Problems (2025)
7 min read Two-Pointer Core Idea Two pointers maintain two indices into a sorted or structured array, moving toward each other or in Read article
System Design
Low-Level Design: Job Board Platform — Job Listings, Search, Applications, and Recruiter Workflow
7 min read Core Entities Company: company_id, name, description, logo_url, website, size, industry, verified (boolean). Job: job_id, company_id, title, description, location, is_remote, employment_type Read article
System Design
System Design: Workflow Engine — DAG Execution, State Persistence, and Fault Tolerance
7 min read What is a Workflow Engine? A workflow engine executes multi-step processes where steps have dependencies, can run in parallel, and Read article
System Design
Low-Level Design: CRM System — Contact Management, Pipeline Tracking, and Activity Logging
5 min read Core Entities Contact: contact_id, first_name, last_name, email (unique), phone, company_id, job_title, source (INBOUND, OUTBOUND, REFERRAL), owner_id (assigned sales rep), created_at, Read article