Algorithms you can see, then play.
Most people find data structures hard because they're invisible. Here, every algorithm moves — step by step, in plain English — and the moment it clicks, you get a problem to prove it.
46 algorithms · 12 problems · no sign-up, ever
Your learning trail
A path built for newbies — each stop unlocks the next. See the full map →
Watch it move
Every step animates with a plain-English line telling you exactly what just happened — and why.
Play with it
Pause, rewind, slow it down, or feed in your own numbers and re-run. It's a sandbox, not a slideshow.
Then prove it
See brute → best for real problems, then write your own solution in the in-browser editor.
Pick a track
🧮 Data Structures & Algorithms
The core curriculum — searching, sorting, hashing, trees, graphs and dynamic programming. 46 algorithms, each one you can watch move, then solve.
Start the track →🏗️ System Design
How real systems stay fast when a million people show up at once — servers, scaling, caching, databases — from zero.
Start the track →⚙️ Operating Systems
How one computer juggles many programs on a single CPU — processes, scheduling, deadlock, memory — watch it happen.
Start the track →🗄️ Databases
How data is stored, found in an instant, and kept correct when many people change it at once — tables, SQL, indexes, transactions, joins.
Start the track →🌐 Networking
How your message crosses the planet and back in under a second — IP, packets, DNS, TCP, HTTPS — watch a website load, step by step.
Start the track →