Low Level Design interview questions, solved properly
The LLD round is where you turn a vague problem into clean classes and working code in under an hour. These walkthroughs show the full object oriented design for each classic problem: the core classes and their responsibilities, how they relate, the design patterns that actually fit, the tricky edge cases, and a code skeleton you can build from. Every page comes with a class diagram so you can see the whole structure at a glance.
Parking Lot
Object-oriented design of a multi-level parking lot with spot types, ticketing, pluggable pricing, nearest-spot allocation, and payment, built to be safe under concurrent entry and exit.
Read the designElevator System
A multi-elevator controller where a dispatcher picks the best car for each hall request and every car runs a SCAN/LOOK scheduler over separate up and down queues driven by a state machine.
Read the designVending Machine
An object-oriented Vending Machine design where the machine moves through Idle, HasMoney, Dispensing and OutOfStock states using the State pattern, with an inventory of product slots and a change-making module for coins and notes.
Read the designMovie Ticket Booking (BookMyShow)
Object-oriented design of a movie ticket booking system where the hard part is locking selected seats with a timeout so two users never book the same seat under concurrency.
Read the designLRU Cache
Design a generic, fixed-capacity LRU (Least Recently Used) cache that supports O(1) get and put by combining a hash map for lookup with a doubly linked list for recency ordering.
Read the design