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Rich Werden

Web Developer & Software Engineer

A site for Rich to write about code and show some completed projects for future reference...

Systems Design Interview Questions

The below list is adapted/augmented from an article on Hackernoon - Top 10 System Design Interview Questions for Software Engineers. Also worth reading is the same author’s article on how to approach answering these sorts of quests. (Imagine all of the below bullet-points have an implied ‘How To’ in front of them if not explicitly written. Thnx.)

1. Design TinyURL or bitly

A URL shortening service

  • How to generate a unique ID for each URL?
  • How would your service handle redirects?
  • How would your service handle caching?
  • How would your service handle duplication of previously submitted URLs?
  • How would you generate unique IDs at scale (thousands of URL shortening requests coming every second)?
  • How to set time-to-live / delete expired URLs etc?
  • User records for those submitting the URLs to be shortened
  • How would you support custom user-defined short URLs?
  • How to track click stats on each link?

2. Design YouTube/Netflix/Twitch

(Possibly-realtime) Video streaming service (aka simultaneously Storing and Transmitting petabytes of data)

  • How to efficiently store large amounts of data
  • How to distribute data in away that a huge number of users can watch simultaneously
  • How to allow for easy sharing of links.
  • How would you record stats about videos (total # of views, up/down-votes, etc.)
  • How would a user add comments on videos (in realtime), how would they be stored
  • User playlists of upcoming videos
  • User history of watched video
  • User Recommended videos process

3. Design Facebook-Messenger/WhatsApp

Global chat service

  • How would you design one-on-one conversations between users?
  • How would you extend your design to support group chats?
  • What to do when a user is not connected to the internet?
  • When to send push notifications?
  • Can you provide end-to-end encryption. How?

4. Designing Quora/Reddit/HackerNews

Message board service w/social network aspects - Users can post text or share links. Then other users can comment or vote on them.

  • Record stats for each answer - category, the total number of views, upvotes/downvotes, etc.
  • Track Users’ histories of votes, submissions, and comments
  • Track Users being able to follow topic or specific other users
  • Create timeline/newsfeed for individual users consisting of top questions from all users, topics they follow, and individuals they follow.

5. Design Dropbox/Google Drive/iCloud

Global file storage & sharing service

  • How would users be able to upload/view/search/share files or photos?
  • How would you track permissions for file sharing
  • How would you allow multiple users to edit the same document

6. Design Facebook/Twitter/Instagram

Large social media service with hundreds of millions of users

  • How to efficiently store and search for posts or tweets.
  • How to Track the relationships of who befriends/follows whom. Especially case of millions of users following a single celebrity.
  • Newsfeed generation

7. Design a Type-Ahead Prediction Service

  • How to do the predictions themselves?
  • How to store previous search queries?
  • How to keep the data fresh?
  • How to find the best matches to the already typed string?
  • How to handle updates and the user is typing too fast?
  • How to forward push loading of most likely result to client before they ask for it?

8. Design a ‘Web Crawler’

Scalable service that can crawl the entire Web and fetch/parse hundreds of millions of Web documents

  • How to store previous search queries? (like#7)
  • How to keep the data fresh? (like#7)
  • How to find new web pages?
  • How to prioritize web pages that change dynamically?
  • How to ensure that your crawler is not infinitely stuck on the same domain or same loop of A->B->C->A->B… ?

9. Design an API Rate Limiter

  • Limit the number of requests an entity can send to an API within a time window e.g., 15 requests per second or only 2000 total requests.
  • Rate limiting should work for a distributed setup, as the APIs are accessible through a cluster of servers and can receive simultaneous requests

10. Design Uber or Lyft

Ride sharing service / a proximity server

  • How to efficiently match nearby customers <–> drivers when a new ride request is made?
  • How to store millions of dynamic geographical locations for drivers and riders who are always moving.
  • How to handle updates to driver/rider locations w/millions of updates every second?
  • How to track Driver and Customer ratings? The distribution of requests for those rating to drivers/customers post-ride.
  • How to track coupon codes?
  • How to track payment completion or issues?
  • How to track ‘demand’ increase and make changes with those dynamic rates?

11. Design Yelp

Nearby Places/Friends kind of like #10

  • How to store locations for millions of people/places
  • How would the users of the service be able to search nearby friends or places?
  • How to rank places (based on the distance + user reviews)
  • How to efficiently store location data according to the population density (e.g. a block in New York City might have more places/people than a small city)

For all of the above: How to handle creating a widget that can be easily embedded into a third party website (Like a facebook-like button, or a Tweet embed)