Problem library

All 4,072 numbered LeetCode problems, with their topic tags. Use it to choose what to practice and to see what Fanpilot covers.

A topic tag tells you what a solution uses, not why that technique fits. Our chapters and lessons explain the why.

How to use it

1. Pick a topic you've studied, and filter to the problems we cover.
2. Try one without looking at its tags.
3. Afterwards, compare your approach with our chapter or lesson.

To test yourself, pick a problem from the same topic that we don't cover. Before you code, write the slow solution, what makes it slow, and the observation that fixes it.

The last column links to the chapters that mention each problem, the lessons that solve it step by step, and its solution page. Most problems don't have a lesson yet, and the list makes those gaps visible.

Where the data comes from

Numbers, titles, links, categories, and tags come from a snapshot of the doocs/leetcode index, which mirrors LeetCode's public data. Problem statements belong to LeetCode, so we link to them rather than copy them. We leave out company lists: they come from paywalled data and go out of date quickly.