Design Online Auction (eBay) - System Design
An online auction looks like “a listing with a current price that goes up,” and if you model it that way you will lose the interview in the …
Read MoreDesign Coinbase (Crypto Exchange) - System Design
“Let users buy and sell crypto” hides two different, both-irreversible problems welded together. Inside the exchange, Coinbase is a matching …
Read MoreDesign Robinhood (Stock Trading Platform) - System Design
“Let a user buy and sell stocks” sounds like a form that writes a row. Then you notice where the money and the shares actually live. …
Read MoreDesign Venmo / P2P Payment - System Design
Venmo looks like a wallet with a Twitter feed bolted on, and that framing is exactly what makes it interesting. The money side demands …
Read MoreDesign GitHub (Code Hosting + PRs) - System Design
“Host code and let people review changes” sounds like a CRUD app with a diff view. It is not. Under the hood you are running a fleet that …
Read MoreDesign LinkedIn (Professional Graph + Feed) - System Design
LinkedIn looks like Twitter with a suit on. It has a feed, it has profiles, people follow each other. So candidates walk in ready to reuse …
Read MoreDesign Tinder (Dating + Matching) - System Design
“Design Tinder” sounds like Instagram with a nicer gesture. Show a photo, swipe left or right, if two people both swipe right they can chat. …
Read MoreDesign Reddit (Communities + Voting) - System Design
Reddit reads like three easy problems stapled together. Posts in communities: a table. Voting: a counter. Comments: a tree. Say it out loud …
Read MoreDesign Stack Overflow / Quora (Q&A) - System Design
Stack Overflow looks like a CRUD app. Post a question, others post answers, everyone votes, one answer gets accepted, and a number next to …
Read MoreDesign Zoom (Video Conferencing) - System Design
People hear “build Zoom” and reach for the WebRTC tutorial: two peers, an SDP exchange, media flows directly, done. That works for a 1:1 …
Read MoreDesign Amazon Shopping Cart - System Design
A shopping cart sounds like a toy problem. “Store a list of item IDs and quantities for a user, let them add and remove, show it back.” You …
Read MoreDesign Migrate 1PB of Data to Cloud - System Design
“Move 1PB to the cloud” sounds like a copy job, and people design it like one: point a script at the source, rsync to an S3 bucket, wait. …
Read MoreDesign Slack (Team Messaging) - System Design
People hear “build Slack” and reach for a chat toy: a messages table, a WebSocket, insert on send, push to whoever is connected. That works …
Read MoreDesign Ads Management & Display in Social Feed - System Design
Everyone models an ad server as a lookup: “the user opens the feed, we fetch an ad, we show it, done.” The interviewer lets that sit for a …
Read MoreDesign Distributed Document Editor (Notion / Wikipedia) - System Design
Almost everyone reaches for Google Docs the moment they hear “document editor,” and almost everyone is answering the wrong question. Google …
Read MoreDesign Toll Collection (FASTag) - System Design
A car drives through a toll lane at 30 km/h, an overhead antenna reads its RFID tag, and by the time the nose of the car reaches the barrier …
Read MoreDesign Flash Sale (6M Free Burgers in 1 Hour) - System Design
“Design a flash sale” sounds like a shopping-cart problem until you write down the actual numbers: Burger King runs a promo, the app has 50 …
Read MoreDesign IRCTC Train Booking (Tatkal) - System Design
“Book a train ticket” sounds like inserting a row. Then you look at Tatkal. At 10:00:00 sharp, a few days’ worth of demand for a scarce …
Read MoreDesign MakeMyTrip Travel Search - System Design
“Design MakeMyTrip” sounds like a shopping app: a user types two cities and a date, a list of flights comes back, they pick one and pay. The …
Read MoreDesign an Authentication & Login System - System Design
“Let users log in” is the request that hides an entire distributed system. You need to store a password without ever storing the password, …
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