LLD interview questions
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How do you approach an LLD interview end-to-end?
Medium · LLD, Fundamentals, Interview
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Explain SOLID principles with an LLD example.
Medium · LLD, Fundamentals, SOLID & OOP
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How do the four OOP pillars apply to LLD? Composition vs inheritance?
Medium · LLD, Fundamentals, SOLID & OOP
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Which design patterns come up most in LLD interviews?
Medium · LLD, Fundamentals, Design Patterns
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UML notation for LLD — what do you actually need on the whiteboard?
Easy · LLD, Fundamentals, Fresher
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Concurrency toolkit for LLD — locks, atomics, queues, executors.
Hard · LLD, Fundamentals, Concurrency
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Thread-safety patterns — immutability, confinement, delegation, copy-on-write.
Hard · LLD, Fundamentals, Concurrency
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Top LLD interview mistakes (and how to avoid them).
Easy · LLD, Fundamentals, Interview
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Design a dependency injection container for services.
Medium · LLD, Fundamentals, SOLID & OOP
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Design DTO vs Entity separation for a REST API layer.
Medium · LLD, Fundamentals, SOLID & OOP
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Design exception hierarchy and error handling for a payment processor.
Medium · LLD, Fundamentals, SOLID & OOP
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Design a PaginatedResult API with offset and cursor-based pagination.
Medium · LLD, Fundamentals, Data Structures
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Design a BankAccount with deposit, withdraw, and balance validation.
Easy · LLD, SOLID & OOP, Fresher
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Design a ShoppingCart with add, remove, and total calculation.
Easy · LLD, SOLID & OOP, Fresher
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Design a Shape hierarchy (Circle, Rectangle, Triangle) with area calculation.
Easy · LLD, SOLID & OOP, Fresher
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Design a Student / Course / Enrollment system with 1:N relationships.
Easy · LLD, SOLID & OOP, Fresher
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Design a PricingStrategy (Regular, Discount, Premium) using Strategy pattern.
Medium · LLD, Design Patterns, Fresher
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Design a NotificationFactory (Email, SMS, Push) using Factory pattern.
Medium · LLD, Design Patterns, Fresher
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Design a StockPrice notifier with multiple subscribers (Observer pattern).
Medium · LLD, Design Patterns, Senior
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Design a Coffee ordering system with add-ons (Decorator pattern).
Medium · LLD, Design Patterns, Senior
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Design a Pizza builder with optional toppings (Builder pattern).
Medium · LLD, Design Patterns, Fresher
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Design an undo/redo text editor (Command pattern).
Medium · LLD, Design Patterns, Senior
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Design a DataExporter (CSV, JSON, XML) using Template Method pattern.
Medium · LLD, Design Patterns, Senior
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Design a middleware pipeline (auth → rate-limit → handler) using Chain of Responsibility.
Medium · LLD, Design Patterns, Senior
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Design a UserRepository with in-memory and database implementations.
Medium · LLD, Design Patterns, Senior
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Design a parking lot system.
Medium · LLD, Machines & Devices, SOLID & OOP
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Design an elevator control system (multi-car, multi-floor).
Hard · LLD, Machines & Devices, Concurrency
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Design a vending machine (State pattern).
Medium · LLD, Machines & Devices, Design Patterns
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Design an ATM system.
Hard · LLD, Machines & Devices, Design Patterns
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Design a thread-safe LRU cache with O(1) get and put.
Medium · LLD, Data Structures, Concurrency
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Design a thread-safe logger (levels + appenders + async).
Hard · LLD, Data Structures, Concurrency
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Design an in-process rate limiter (Token Bucket + Sliding Window).
Hard · LLD, Data Structures, Concurrency
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Design an in-memory file system (Composite pattern).
Medium · LLD, Data Structures, Design Patterns
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Design a TaskQueue with producer-consumer and worker thread pool.
Hard · LLD, Data Structures, Concurrency
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Design an in-memory key-value store with TTL and eviction.
Hard · LLD, Data Structures, Concurrency
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Design an in-process pub-sub message broker with topics.
Hard · LLD, Data Structures, Concurrency
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Design a thread-safe ConcurrentMap with striped locking.
Hard · LLD, Data Structures, Concurrency
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Design a SharedResource with read-write lock for concurrent access.
Hard · LLD, Data Structures, Concurrency
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Design a movie ticket booking system (BookMyShow).
Hard · LLD, Booking & Reservation, Concurrency
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Design an online hotel booking system.
Hard · LLD, Booking & Reservation, Concurrency
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Design a library management system.
Medium · LLD, Booking & Reservation, SOLID & OOP
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Design a restaurant management system.
Medium · LLD, Booking & Reservation, Concurrency
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Design a cab booking system (Uber / Ola).
Hard · LLD, Booking & Reservation, Architect
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Design a meeting scheduler / calendar with conflict detection.
Medium · LLD, Booking & Reservation, Data Structures
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Design an online auction system with bidding and winner selection.
Hard · LLD, Booking & Reservation, Concurrency
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Design Splitwise (group expense sharing).
Hard · LLD, Financial & Ledger, Design Patterns
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Design StackOverflow (Q&A + reputation).
Hard · LLD, Platforms & Social, Design Patterns
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Design a notification service (email / SMS / push, retries).
Hard · LLD, Platforms & Social, Concurrency
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Design a Twitter-like social feed with fan-out on write.
Hard · LLD, Platforms & Social, Data Structures
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Design clean architecture layers (domain, application, infrastructure).
Medium · LLD, Architecture & Frameworks, Staff
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Design a PaymentGateway using hexagonal architecture (ports & adapters).
Medium · LLD, Architecture & Frameworks, Staff
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Design lightweight CQRS with separate read/write models for Orders.
Medium · LLD, Architecture & Frameworks, Staff
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Design an idempotent Payment API with deduplication keys.
Medium · LLD, Architecture & Frameworks, Staff
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Design an immutable AuditLog for entity change tracking.
Medium · LLD, Architecture & Frameworks, Staff
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Design an Order lifecycle state machine (Placed → Paid → Shipped → Delivered).
Medium · LLD, Architecture & Frameworks, Design Patterns
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Design a resilient ExternalAPIClient with retry and circuit breaker.
Medium · LLD, Architecture & Frameworks, Staff
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Design a UserProfileService with cache-aside and write-through patterns.
Medium · LLD, Architecture & Frameworks, Staff
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Design backward-compatible API versioning (v1 / v2 evolution).
Medium · LLD, Architecture & Frameworks, Staff
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Design an extensible ReportGenerator with plugin registry.
Hard · LLD, Architecture & Frameworks, Staff
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Design a configurable discount/pricing rule engine.
Hard · LLD, Architecture & Frameworks, Staff
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Design a tenant-isolated DataAccess layer for multi-tenant SaaS.
Hard · LLD, Architecture & Frameworks, Architect
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Design a cron-like job scheduler with priority, retry, and dead-letter.
Hard · LLD, Architecture & Frameworks, Architect
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Design DDD tactical patterns — aggregates, value objects, domain services.
Medium · LLD, Architecture & Frameworks, Architect
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Design bounded context mapping for Order, Inventory, and Payment.
Medium · LLD, Architecture & Frameworks, Architect
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Design an anti-corruption layer between legacy and new billing systems.
Medium · LLD, Architecture & Frameworks, Architect
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Design a mini web framework (router, middleware chain, DI container).
Hard · LLD, Architecture & Frameworks, Architect
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Design a runtime feature flag framework with targeting rules.
Medium · LLD, Architecture & Frameworks, Architect
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Design a custom serialization framework with schema registry.
Hard · LLD, Architecture & Frameworks, Architect
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Design a chess game with move validation.
Hard · LLD, Games & State, Design Patterns
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Design Tic-Tac-Toe (N×N).
Easy · LLD, Games & State, SOLID & OOP
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Design Snakes & Ladders.
Easy · LLD, Games & State, Fresher
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Design a deck of cards (foundations for poker/blackjack).
Easy · LLD, Games & State, SOLID & OOP