Search: train

Low-Level Design: Gym Membership and Access Control System — Plans, Check-In, and Class Booking

⏱ 4 min read Core Entities Member: member_id, user_id, first_name, last_name, email, phone, photo_url, join_date, status (ACTIVE, SUSPENDED, CANCELLED, FROZEN), emergency_contact. MembershipPlan: plan_id, name […] Read article

Apr 17, 2026 System Design

Low-Level Design: Fleet Management System — Vehicle Tracking, Maintenance, and Route Optimization

⏱ 5 min read Core Entities Vehicle: vehicle_id, vin (unique), make, model, year, type (SEDAN, VAN, TRUCK, ELECTRIC), status (AVAILABLE, ASSIGNED, IN_MAINTENANCE, OUT_OF_SERVICE), current_driver_id, […] Read article

Apr 17, 2026 System Design

Low-Level Design: Online Judge System — Submission Processing, Sandboxed Execution, and Scoring

⏱ 5 min read Core Entities Problem: problem_id, title, slug, difficulty (EASY, MEDIUM, HARD), statement_markdown, constraints, time_limit_ms, memory_limit_mb, tags (array), is_active. TestCase: tc_id, problem_id, […] Read article

Apr 17, 2026 System Design

System Design: Payment Gateway — Authorization, Settlement, Idempotency, and Fraud Prevention

⏱ 5 min read Requirements A payment gateway processes card transactions between merchants and issuing banks. Core flow: customer enters card details → merchant […] Read article

Apr 17, 2026 System Design

Advanced Recursion and Backtracking Interview Patterns: N-Queens, Sudoku, Expression Add Operators (2025)

⏱ 5 min read Backtracking Framework Backtracking = DFS + pruning. The general framework: choose a candidate for the next position, recurse, undo the […] Read article

Apr 17, 2026 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

Apr 17, 2026 Algorithms

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

Apr 17, 2026 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

Apr 17, 2026 System Design

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

Apr 17, 2026 Algorithms

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

Apr 17, 2026 System Design