State pattern
A shop ledger page, 1899. Every line adds up.
LLD Series: Elevator System (LLD)
Design an elevator system for a building with N floors and M elevators. Users press hall buttons (floor + direction) and cabin buttons (destination). Decide which elevator serves a request, and how...
12 min read
LLD Series: Vending Machine (Low-Level Design)
Design a vending machine. A user inserts coins/notes, selects a product, the machine dispenses it and returns change. Handle sold-out items, insufficient money, cancellation and refunds.
16 min read
LLD Series: ATM (Low-Level Design)
Design an ATM. A user inserts a card, enters a PIN, and can withdraw cash, deposit or check balance. The machine must dispense the right notes. Model the machine's behaviour so that invalid...
19 min read