Each problem gives you requirements and an empty canvas. Every box you add gets a verdict, and changing the scale shows you which ones flip.
Problem 01easy
Users shorten long URLs and get a short link; anyone with the link is redirected. ~10M DAU, reads dwarf writes.
Features
Starting scale
Problem 02easy
Users paste a block of text and get a short link to share it; anyone with the link can read it. Reads outnumber writes about 10 to 1.
Features
Starting scale
Problem 03medium
Cap how many requests each client can make to your API, say 100 a minute, and reject the rest. Every single request has to be counted.
Features
Starting scale
Problem 04medium
Users click ads and land on the advertiser's site. Every click is recorded, and advertisers see clicks per ad per minute. Clicks are billed, so a lost click is lost money.
Features
Starting scale
Problem 05medium
Users upload files from any device, download them anywhere, and see changes sync to their other devices. Files can be up to 50 GB.
Features
Starting scale