Low-Level Design
System Design › Low-Level DesignDesign an LRU Cache (O(1) get & put) — Low-Level Design
Design an LRU cache with O(1) get and put — the classic data-structure question. Combining a HashMap with a doubly-linked list, sentinel nodes, Java code, and the thread-safety / LinkedHashMap notes.
System Design › Low-Level DesignDesign Splitwise / Expense Sharing (Low-Level Design)
Design an expense-sharing app like Splitwise in an LLD interview: split strategies (equal/exact/percentage), the who-owes-whom balance model, and the debt-simplification bonus. Classes, UML, and design decisions.
System Design › Low-Level DesignDesign BookMyShow / Movie Booking (Low-Level Design)
Design a movie ticket booking system in an LLD interview — the concurrency-focused version. Modelling Movie/Show/ShowSeat, and the reserve-then-confirm seat locking that prevents double-booking. Classes, UML, decisions.
System Design › Low-Level DesignDesign a Vending Machine (Low-Level Design)
Design a vending machine in an LLD interview — the textbook State pattern problem. States (Idle, HasMoney, Dispensing, OutOfStock), inventory, the change algorithm, classes, UML, and key decisions.
System Design › Low-Level DesignDesign an Elevator System (Low-Level Design)
Design an elevator system in an LLD interview: modelling each elevator as a state machine with the SCAN movement algorithm, a controller that dispatches requests via a pluggable scheduling strategy, classes, and UML.
System Design › Low-Level DesignDesign a Parking Lot (Low-Level Design / OOD)
The classic machine-coding LLD question solved end to end: requirements, the class design (ParkingLot, Level, Spot, Vehicle, Ticket), UML relationships, and the patterns that impress — Strategy, Factory, Singleton.
System Design › Low-Level DesignChain of Responsibility Pattern in Java (Example)
The Chain of Responsibility pattern explained: pass a request along a chain of handlers until one handles it, decoupling sender from receiver. Servlet filters, approval workflows, Java code, UML, when to use.
System Design › Low-Level DesignTemplate Method Pattern in Java (with Example)
The Template Method pattern explained: define an algorithm's fixed skeleton in a base class and let subclasses fill in the varying steps. The Hollywood Principle, Template Method vs Strategy, Java code and UML.
System Design › Low-Level DesignCommand Pattern in Java (with Undo Example)
The Command pattern explained: wrap a request as an object with execute() and undo(), decoupling invoker from receiver — unlocking undo/redo, queuing, logging, and macros. Java code, UML, when to use.