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Courses, docs and graded problems in one place. Every lesson is free to read; an account only keeps your progress.
Everything you need to go from reading about a system to proving you can build part of it.
6 pages to read
Lessons, docs and articles are open to everyone. No account, no paywall.
11 languages
A real editor with syntax highlighting, in Python, C++, Java, Go, Rust and six more.
2 graded problems
Each submission runs in a fresh container with no network, against tests you cannot see.
Saved to your account
Sign in and your solved problems, finished lessons and notes are kept for you.
Structured paths you work through in order, chapter by chapter.
Every one is graded against hidden tests in an isolated sandbox. A wrong answer shows the failing input.
What people ask before they start.
Yes. Every course, doc, article and problem statement is free to read without an account.
To run code and keep your progress: submissions, solved problems, completed lessons, bookmarks and notes are saved to it.
Python, C, C++, Java, JavaScript, TypeScript, Go, Rust, Ruby, PHP and Bash. Each problem lists the ones it accepts.
In a fresh, isolated container with no network access and strict time and memory limits. It is thrown away as soon as the run finishes.
So a solution has to be correct in general, not just on the examples. When a submission fails, you still see the verdict and how many tests passed.