Python runs in your browser
Everything you need to be interview ready, in one place you can run.
A complete data-structures and algorithms course that starts at “what is a variable” and ends at system design. Read a lesson, edit the examples, run them, and practise against 315 problems, without leaving the page or opening a terminal.
Free, open source, and nothing to sign up for. Your progress stays in your own browser.
- 29
- lessons, written from scratch
- 315
- problems, indexed and explained
- 75
- drills, graded automatically
- 104
- terms defined in plain English
How it works
The order matters. Most people fail interviews because they practised problems before they had the foundations to see the pattern.
- 01
Read the lesson
Every topic is taught from first principles, not summarised from somewhere else. You learn why a hash map trades space for time before you are asked to use one.
- 02
Run the code where you read it
Python runs inside the page. Edit any example, press Run, and read the real output. No terminal, no install, and tracebacks are shown exactly as Python wrote them, because reading them is a skill.
- 03
Practise until it is automatic
75 graded drills build the syntax reflexes first. Then work the problem index in NeetCode order, with a 22-minute timer and the analysis template that interviewers actually want to hear.
The roadmap
21 lessons in the order they should be read.
- 0000 — Python From Zero29 min63 runnable
- 0101 — Foundations32 min20 runnable
- 0202 — Arrays, Hashing, Two Pointers, Sliding Window20 min15 runnable
- 0303 — Stacks, Queues, Binary Search, Linked Lists19 min16 runnable
- 0404 — Trees, Tries, Heaps23 min13 runnable
- 0505 — Backtracking & Graphs21 min11 runnable
- 0606 — Dynamic Programming21 min16 runnable
- 0707 — Greedy, Intervals, Bit Manipulation, Math18 min7 runnable
- 0808 — Interview Craft: Being Smarter and Faster17 min
- 0909 — Systems: LLD, HLD, SQL, Backend16 min1 runnable
- 1010 — Resources5 min
- 1111 — Advanced Algorithms & The Gaps34 min26 runnable
- 1212 — Complete Problem Index39 min1 runnable
- 1313 — Low-Level Design, In Depth26 min11 runnable
- 1414 — High-Level Design, In Depth21 min
- 1515 — Databases, End to End22 min
- 1616 — CS Fundamentals: OS, Networking, Concurrency, Python Internals20 min4 runnable
- 1717 — Your Practice Environment8 min
- 1818 — CodeSignal OA: The 5-Day Sprint10 min
- 1919 — Prerequisites, Math & Glossary17 min
- 2020 — Learning Platform: Build Specification14 min
Taking a graduate algorithms class? The course track adds 8 proof-first lessons, from asymptotics through NP-completeness.