Low Level Design Sheet
The Low Level Design sheet covers object-oriented modelling at the class level: SOLID principles, the classic design patterns, concurrency primitives and the machine-coding rounds that ask you to build a small working system in an hour.
The sheet holds 12 patterns and 46 topics, tracked row by row. From any row you can read the theory for a topic, solve the mapped problem in the browser, sit a mock interview on it, have the AI coach teach it back to you, keep notes, bookmark a row and mark it done. Progress is saved against your account, so the sheet is also the record of what you have already covered.
Looking for the course? Low Level Design course teaches the same families as theory and lessons, rather than a progress checklist.
Who it is for
It suits engineers facing a machine-coding or object-design round, and anyone whose classes work but grow hard to change. Familiarity with one object-oriented language is assumed; the patterns are language-neutral.
How to work through it
Read the principle, then refactor something towards it. Every problem here is runnable, so the honest test of an abstraction is whether the code still compiles and the tests still pass after you have applied it.
Practice runs on the same platform as the sheet: 850+ problems across every track, code execution in 6 languages, and AI mock interviews that follow the pattern you are studying rather than a random question.
What the low level design sheet covers
Interview Soon (~20h)
8 patterns that cover 80% of LLD interviews
- OOP Foundations & Class Design — OOP Pillars & Class Relationships, SOLID Principles, Entity Modeling & Schema Design
- Strategy & Factory Patterns — Strategy Pattern, Factory & Abstract Factory, Builder, Prototype & Object Pool, Bridge, Flyweight & Composite Deep Dive
- State Pattern & State Machines — State Pattern, Case Study: Design a Vending Machine, Visitor, Memento & Specification
- Observer, Decorator & Behavioral — Observer Pattern, Decorator & Chain of Responsibility, Case Study: Command Pattern & Text Editor, Mediator, Iterator & Null Object
- Concurrency Patterns — Thread Safety & Synchronization, Producer-Consumer & Thread Pools, Lock-Free Structures & Advanced Concurrency, Actor Model, CSP & Reactive
- Machine Coding & Interview Execution — The LLD Interview Framework, Pattern Recognition & Application
- Case Studies — Foundational — Design a Parking Lot System, Design an Elevator System, Design Movie Ticket Booking (BookMyShow), Design Splitwise / Expense Sharing, Design Snake-and-Ladder, Design a Rate Limiter
- Case Studies — Applied — Design LRU Cache, Design a Notification System, Design Chess, Design a Food Delivery System
Deep Dive (~40h additional)
4 patterns for deep expertise and senior-level interviews
- Advanced Case Studies — Thread-Safe LRU Cache, Design a Pub-Sub System, Design a Task Scheduler, Design a Digital Wallet, Design Ride Sharing (Uber/Ola), Design Online Shopping Cart, Design Hotel/Meeting Room Booking, Design In-Memory File System
- Domain-Specific Patterns — Financial System Patterns, Progressive Design Problems (Coinbase-Style), Game Design Patterns
- Machine Coding Mastery — Company-Specific LLD Preparation, Event-Driven & Schema Patterns
- Architecture Teardowns — Spring Framework — IoC Container Internals, Java Collections — Patterns Inside, Python Data Model — Magic Methods as Patterns
