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Practice

Predict-the-output puzzles, spot-the-bug katas, review-the-AI's-code exercises, interview banks and flashcards, every one built from a topic you can open next to it. Scores stay in this browser.

1733 items 22 tracks runs offline

kata todaySpot the bug · C#Spot the bug in the callback loopDelegates turn methods into type-safe values; events restrict who can publish notifications. Learn invocation lists, identity, capture, and async boundaries.Start · 4 min

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py Python 139 exercises · Predict the output 25 · Spot the bug 18 · Review AI code 19 · Quiz 63 · Fill in 14 js JavaScript 184 exercises · Predict the output 43 · Spot the bug 30 · Review AI code 30 · Quiz 65 · Fill in 16 ts TypeScript 76 exercises · Predict the output 15 · Spot the bug 15 · Review AI code 15 · Quiz 31 go Go 106 exercises · Predict the output 17 · Spot the bug 15 · Review AI code 13 · Quiz 42 · Fill in 19 rs Rust 75 exercises · Predict the output 20 · Spot the bug 15 · Review AI code 15 · Quiz 25 cs CS foundations 164 exercises · Predict the output 23 · Spot the bug 23 · Review AI code 23 · Quiz 83 · Fill in 12 llm AI and LLM engineering 75 exercises · Predict the output 7 · Spot the bug 7 · Review AI code 7 · Quiz 35 · Fill in 19 arch Architecture and system design 25 exercises · Predict the output 5 · Spot the bug 5 · Review AI code 5 · Quiz 10 api Backend 139 exercises · Predict the output 26 · Spot the bug 27 · Review AI code 26 · Quiz 60 c# C# 88 exercises · Predict the output 29 · Spot the bug 19 · Review AI code 16 · Quiz 24 cpp C++ 92 exercises · Predict the output 19 · Spot the bug 18 · Review AI code 18 · Quiz 37 ai Coding in the AI era 101 exercises · Predict the output 18 · Spot the bug 18 · Review AI code 18 · Quiz 47 db Data and databases 5 exercises · Predict the output 1 · Spot the bug 1 · Review AI code 1 · Quiz 2 ds Data science 31 exercises · Predict the output 6 · Spot the bug 5 · Review AI code 5 · Quiz 15 ops DevOps and cloud 15 exercises · Predict the output 3 · Spot the bug 3 · Review AI code 3 · Quiz 6 ui Frontend 82 exercises · Predict the output 10 · Spot the bug 11 · Review AI code 10 · Quiz 37 · Fill in 14 game Game development 26 exercises · Predict the output 5 · Spot the bug 5 · Review AI code 5 · Quiz 11 jvm Java 81 exercises · Predict the output 17 · Spot the bug 16 · Review AI code 16 · Quiz 32 kt Kotlin 66 exercises · Predict the output 18 · Spot the bug 12 · Review AI code 12 · Quiz 24 php PHP 69 exercises · Predict the output 19 · Spot the bug 12 · Review AI code 12 · Quiz 26 sec Security 26 exercises · Predict the output 5 · Spot the bug 5 · Review AI code 5 · Quiz 11 swift Swift 68 exercises · Predict the output 15 · Spot the bug 13 · Review AI code 13 · Quiz 27