LLD

1. Low-level design overview Practical map of LLD/OOD interviews: what they test, how they differ from system design, regional format quirks, and how interviewers score you.
2. LLD delivery framework (35 min) Step-by-step LLD interview pacing: requirements, entities, class design, implementation, and extensibility — with Tic-Tac-Toe as the running example.
3. OOP for LLD interviews Encapsulation, abstraction, polymorphism, and inheritance — with interview-shaped bad/good examples and a bias toward composition.
4. LLD guidelines & STAR narration KISS, DRY, YAGNI, separation of concerns, Law of Demeter, SOLID for interviews, STAR as LLD narration, and when to reach for a basic pattern.
5. Design patterns for LLD Creational, structural, and behavioral patterns worth knowing for interviews: Factory, Builder, Singleton caveats, Decorator, Facade, Strategy, Observer, State.
6. Hub — LLD principles & patterns Routing hub for Lattice LLD: when to open OOP & principles, guidelines/STAR, or design patterns — with a quick “when to use each” map.
7. Concurrency in LLD — map Shared-memory concurrency for interviews: threads vs processes, the primitive toolbox, language cheat sheet, and three problem families — correctness, coordination, scarcity.
8. Correctness: locks & check-then-act Stop data corruption under concurrency: coarse and fine locks, read-write locks, atomics, thread confinement, check-then-act, and read-modify-write — with a decision tree.
9. Coordination: queues & backpressure Producer-consumer for LLD: why busy-wait fails, blocking queues, backpressure, graceful shutdown, actors, async requests, and burst buffering.
10. Scarcity: semaphores & pools Manage limited resources in LLD: semaphores for concurrent ops and budgets, blocking-queue pools for connections/GPUs, timeouts, and utilization techniques.
11. Hub — LLD concurrency Decision-tree hub for Lattice LLD concurrency: basics, correctness, coordination, and scarcity — which post to open for shared state, handoffs, and limited pools.
12. LLD classics index Full Lattice index of classic LLD deep dives — every walkthrough linked, a recommended practice order, and the concurrency note interviewers poke per classic.
13. Design a parking lot Parking lot LLD: motorcycle/car/large spots, ticket on enter, hourly fee in cents with round-up, relational occupancy set, enter/exit APIs, verification, and multi-floor / concurrency extensions.
14. Design a rate limiter (LLD) In-memory API gateway rate limiter LLD: per-endpoint configs, LimiterFactory + Strategy, Token Bucket and Sliding Window Log, RateLimitResult, then concurrency, hot config, and memory eviction as extensions.
15. Design an elevator system Elevator LLD with simulation step(): 3 cars, 10 floors, hall UP/DOWN vs DESTINATION requests, selectBestElevator, SCAN algorithm cases, verification tick trace, and concurrency/express extensions.
16. Hub — parking, limiter, elevator Practice hub for parking lot, in-memory rate limiter, and elevator — order to drill, concurrency callouts, and links into each complete-solution section.
17. Design Amazon Locker Full LLD for Amazon-style lockers: clarifying questions, exact-size match, 7-day TTL, staff openExpired, Locker/Compartment/AccessToken design (Package is not an entity), deposit/pickup flows, and extensibility.
18. Design movie ticket booking BookMyShow-style LLD: search and browse, Showtime owns reservations as seat state, per-showtime locking so concurrent books have one winner, cancel by confirmation ID, then checkout holds and dynamic showtimes as extensions.
19. Design BookMyShow BookMyShow LLD: City→Cinema→Screen→Show hierarchy, three-state seats (AVAILABLE → LOCKED → BOOKED) with TTL holds, payment stub, booking confirmation, per-show locking, and pricing as an extension.
20. Design inventory management Multi-warehouse inventory LLD: add/remove/transfer with no-negative stock, availability queries, per-warehouse low-stock Observer alerts, coarse locks + ordered multi-lock transfers, then reservations and in-transit Transfer holders.
21. Design a library system Full interview walkthrough for a library management system: Book vs BookItem, catalog search, checkout/return with due dates and fines, reservation queues, and extensibility.
22. Hub — booking, inventory, locker Practice hub for BookMyShow, movie booking, inventory, Amazon locker, and library — shared claim/commit skeleton, concurrency callouts, complete-solution links.
23. Design Tic Tac Toe Full interview walkthrough for Tic Tac Toe: clarifying dialogue, Game/Board/Player design, makeMove and eight-line win checks, verification trace, and extensibility (NxN, undo, bot).
24. Design Connect Four Full interview walkthrough for Connect Four: clarifying dialogue, Game/Board/Player design, makeMove and direction-vector win checks (no WinChecker Strategy), verification trace, and extensibility.
25. Design a chess game Full interview walkthrough for designing a chess game: clarifying dialogue, Game/Board/Piece polymorphism, pseudo-legal vs legal moves, check/mate, verification, and extensibility (castling, undo, AI).
26. Design a logger In-process logging library LLD: LogRecord, per-destination level + format, Formatter × Sink composition, per-destination locks, sink-failure handling, then async queues and hierarchical named loggers as extensions.
27. Design an in-memory filesystem In-memory FS LLD: FileSystemEntry / File / Folder / FileSystem, path helpers, CRUD + rename/move with cycle detection, bidirectional parent links, verification, and locking strategies for concurrency.
28. Hub — filesystem, logging, games Practice hub for filesystem, logger, Connect Four, Tic Tac Toe, and Chess — practice order, concurrency callouts, and complete-solution links.

Lattice