Problem library
Browse every challenge by difficulty, or return to the guided path when you want a recommendation.
URL Shortener
Turn long links into short codes — and survive the read storm.
Distributed Rate Limiter
Throttle abusive traffic without throttling yourself.
Pastebin
Share text snippets via short links — and survive the front page.
Image Hosting
Host images at internet scale — the edge does the heavy lifting.
Weather API
A public forecast API where caching is the whole product.
Game Leaderboard
Rank millions of players in real time — and keep the top-100 page instant.
Status Page
Hosted status pages — and the read storm that hits the moment they're needed most.
Live Polling App
Audience voting for live TV — a vote burst and a hot result read, at the same second.
User Profile Service
The service every other feature calls — reads at 50:1, and it can't go down.
Feature Flags
Flag evaluation on the hot path of every request — it has to feel free.
Session Store
Every request pays this lookup — it has to be nearly free.
Blog Platform
Publish long-form posts — and let a viral one be free marketing, not an outage.
News Feed / Timeline
Fan out posts to millions — without melting on reads.
Real-time Chat
Deliver messages instantly, in order, online or off.
Web Crawler
Crawl billions of pages — fast, polite, and without repeating yourself.
Search Autocomplete
Suggest as they type — in under 100 milliseconds, every keystroke.
Notification System
Push, SMS and email to millions — without dropping a beat.
E-commerce Catalog
Browse and search a product catalog — and survive your own sale email.
Shopping Cart
Read on every page view, written on every click, and it can never lose an item.
Hotel Booking
Search-heavy availability lookups feeding a contended reservation path.
Ticket Booking
An on-sale stampede where a queue is the waiting room, not a failure.
Food Delivery
Order placement shares the fleet with a nonstop courier-location firehose.
Email Service
Accept every send instantly — and deliver it without dropping a message.
Metrics & Monitoring
Never drop a data point — and keep dashboards fast while the firehose spikes.
Job Scheduler
Enqueue instantly, execute reliably — even when every cron fires at once.
Social Graph
Follow/follower lookups so hot that every feature depends on the cache in front of them.
API Gateway
Auth, routing, and caching for every partner call — thin, but in front of everything.
Video Streaming
Serve petabytes of video to the planet without buffering.
Ride Sharing
Match riders to drivers in real time across a city.
File Storage & Sync
Store, sync and share files across every device — like Dropbox.
Payment System
Move money exactly once — never drop it, never double-charge.
Ad Click Aggregator
Count a firehose of clicks in real time — and lose none of them.
Stock Exchange
Match orders in milliseconds — a slow fill is a wrong fill.
Flash Sale
A 100x drop-day stampede — sell out without overselling.
Collaborative Docs
Google-Docs-style editing — every keystroke, broadcast live, forever.
Live Streaming
Twitch-style live video — one big streamer, a whole city watching.
Multiplayer Game Backend
Hold a 50ms tick budget through launch day.
Fraud Detection
Score every checkout in real time — before the payment ships.
Recommendation Engine
Homepage recommendations, precomputed offline and served hot.
Search Engine
Query serving and continuous indexing, sharing an index without sharing a bottleneck.
Object Storage
An S3-shaped store: durable bytes on one path, fast metadata on the other.
IoT Telemetry
Swallow a device-fleet firehose without dropping a datapoint.