The lineup

Practice problems.

22 real system-design problems. Each is a guided, multi-step drill that ends in a simulated hiring verdict.

Brush up on fundamentals

Starter

4

Starter

Design Comment System

Thread millions of comments under hot posts, keep reads fast, and stop spam from flooding the timeline.

Starter

Design Pastebin

Store and serve arbitrary text blobs at scale with expiry, and decide what belongs in blob storage versus a database.

Starter

Design Rate Limiter

Decide allow-or-reject for every request in a millisecond with token buckets, sliding windows, and distributed counters.

Starter

Design URL Shortener

Turn billions of long URLs into short codes and redirect them in under 50ms, without collisions.

Intermediate

6

Intermediate

Sync files across devices with chunking and dedup, and resolve conflicts when two edits collide.

Intermediate

Design Google Calendar

Model events, recurrence, and invites, and detect scheduling conflicts across time zones.

Intermediate

Design LeetCode

Run untrusted code safely in sandboxes and judge submissions against test cases at scale.

Intermediate

Swipe, match, and recommend at scale, with geospatial sharding and the double-opt-in 'it's a match' problem.

Intermediate

Design Typeahead Suggestion

Return search suggestions in under 100ms as the user types, using tries, caching, and ranking by popularity.

Intermediate

Design Webhook Delivery System

Deliver events reliably to third-party endpoints with retries, backoff, ordering, and at-least-once guarantees.

Advanced

8

Advanced

Design Google Maps

Store the planet's road network and compute shortest paths across a graph with billions of edges.

Advanced

Design Spotify Top-K

Find the top-K trending tracks over a stream of billions of plays without storing every event.

Advanced

Design Ticketmaster

Sell limited seats to a stampede of buyers without overselling, using holds, locking, and fairness.

Advanced

Fan out tweets to millions of followers, and solve the celebrity problem that breaks the naive design.

Advanced

Match riders to nearby drivers in real time with geospatial indexing and live location updates.

Advanced

Design WhatsApp

Deliver messages instantly with read receipts, presence, and ordering across a user's devices.

Advanced

Search millions of businesses by location and rating with geospatial indexes and read-heavy caching.

Advanced

Ingest, transcode, and stream video to a global audience with a CDN and adaptive bitrate.

Expert

4

Expert

Design Collaborative Editing

Let many people edit one document live, using CRDTs or OT for conflict-free convergence.

Expert

Design Distributed Message Queue

Build the queue everyone else depends on, with partitioning, ordering, and durable delivery.

Expert

Design Job Scheduler

Run millions of jobs at the right time with retries, idempotency, and exactly-once semantics.

Expert

Design Realtime Monitoring

Ingest a firehose of metrics, aggregate over time windows, and alert the moment SLOs burn.