Practice coding exercises

Choose a language, then pick a challenge to start. Your code runs in a real runtime and an AI reviewer explains what to fix.

Available languages: JavaScript, Python, Java, TypeScript, C#, C++, HTML, CSS.

170 exercises across three levels — 56 easy, 69 medium, 45 hard — including the interview classics: Two Sum, Valid Parentheses, Reverse Linked List, Climb Stairs and Valid Anagram.

JavaScript solutions are executed against real test cases and marked case by case, showing the input, what was expected and what your code returned.

Nothing is installed locally. The editor, the runtime and the reviewer all run from this page.