Practice series
Inventory, reservations & queues
Limited supply, holds, queues, booking flows, ticketing, auctions, and oversell control.
- 01Preview
Auction (eBay)
Design an eBay-style auction system — bidders compete on live listings under heavy contention near closing time, and the system must never accept a losing bid a...
eBay - 02Preview
Collaborative Shopping
Design a collaborative shopping experience where multiple people share a single cart in real time, add and remove items concurrently, and one designated partici...
Practice bank - 03Preview
Donation Platform
Design a donation platform like GoFundMe — a campaign can go viral overnight and receive a massive spike of small donations, and every dollar must be captured,...
Practice bank - 04Preview
Flash Sale
Design a flash sale system where a limited quantity of a hot item goes on sale at a fixed instant and receives a 1000x traffic spike in seconds — inventory must...
Practice bank - 05Preview
Flight Booking System
Design a flight booking system that lets travelers search and book multi-leg itineraries across airlines, reserving fare-class seat inventory and issuing ticket...
Duffel - 06Preview
Hotel Reservation (Booking.com)
Design Booking.com — a hotel marketplace aggregating live availability and pricing from thousands of independent supplier hotels, where search results must stay...
Booking.com - 07Preview
Hotel Reservation
Design a single-chain hotel reservation engine — travelers search date-range availability across properties, place a hold, and confirm a booking without ever ov...
Practice bank - 08Preview
Job Scheduler
Design a distributed job scheduler (a cron-as-a-service system) that lets tenants register recurring and one-off jobs, guarantees each job fires close to its sc...
Airbnb - 09Preview
Moderation Service
Design a content moderation pipeline that screens user-submitted posts/media for policy violations, balancing posting latency against review accuracy at platfor...
LinkedIn - 10Preview
Restaurant Reservation
Design an OpenTable-style restaurant reservation system where diners book a time slot and party size at a restaurant, restaurants optimize table assignment, and...
Yelp - 11Preview
Spend Management System
Design a corporate spend management platform like Brex or Ramp — every card swipe must be authorized or declined against a live policy engine in under two secon...
Brex - 12Preview
Ticketmaster (General Admission)
Design Ticketmaster for general-admission events — there is no seat map, only a fixed capacity count per ticket tier, and the system must sell tickets correctly...
Ticketmaster - 13Free
Ticketmaster
Design Ticketmaster — an event ticketing system that sells reserved seats under extreme flash-sale contention without ever double-selling a seat.
Ticketmaster - 14Free
Web Crawler
Design a web-scale crawler that politely fetches and indexes billions of pages, deduplicates content, and keeps the corpus fresh.
Google - 15Preview
Webhook
Design a webhook delivery platform (Stripe-webhooks-style) that reliably delivers event notifications to thousands of third-party consumer endpoints under retry...
Stripe - 16Preview
YouTube
Design YouTube’s upload and processing pipeline — accept massive volumes of user-generated video uploads and transform them into a playable, multi-resolution ca...
YouTube - 17Free
LLM Inference Gateway
Design an LLM inference gateway that sits between internal product teams and multiple model providers/backends, handling routing, streaming, quotas, and safety...
OpenAI / Anthropic - 18Preview
ML Feature Store
Design an ML feature store that serves the same features to both offline model training and low-latency online inference for a company like Uber.
Uber - 19Preview
LLM Evaluation Platform
Design the evaluation platform for an organization shipping LLM features: manage a versioned golden set (stratified production samples, an adversarial library,...
Practice bank - 20Preview
Distributed Message Queue
Design a Kafka-style durable, partitioned log broker that ingests high-throughput event streams.
Apache Kafka (LinkedIn) - 21Preview
Online Judge
Design a LeetCode-style online judge that safely runs untrusted user code at scale.
Google / Amazon