LeetKnight

Scaffold, test, and submit LeetCode problems in Java — with an Anki-inspired rating step that drives a hardest-first practice queue.

[!WARNING] Under active development. LeetKnight is pre-1.0. Commands, data-file schemas (.leetknight/reviews.json, per-problem .leetknight.json), and the rating workflow may change between versions without a migration path. Feedback and issue reports are welcome.

What it does

LeetKnight is a VS Code extension for interview prep on LeetCode in Java. It:

• Scaffolds problems locally — pick from the LeetCode catalog (or paste a URL) and it creates <slug>/Solution.java with the official Java starter (plus a Time/Space complexity header) alongside <slug>/notes.md with the problem description.
• Runs & submits from the editor — ▶ runs your solution against LeetCode's own example test cases via the "Run Code" endpoint; ☁️ submits it for real. Both use LeetCode's java runtime — nothing is compiled locally.
• Grades your recall — after every Accepted submission, a modal asks you to rate the attempt (Hard / Medium / Easy). Ratings drive the practice panel, grouped 🔴 Hard → 🟡 Medium → 🟢 Easy so the ones you found hardest sit at the top. Within a group the oldest attempts come first so you don't see the same problem every session.
• Re-solves on demand — click any problem in the panel and it opens Solution.java and resets it back to the starter (no confirmation prompt) so you can re-solve it from scratch. The random-pick button picks one at random (interview-mode: no idea what's coming).
• Scratch pad — playground/Playground.java is a throwaway main you can compile and run locally with ▶ from the editor toolbar. Handy for trying a helper, a data-structure API, or a small algorithm before wiring it into a problem's Solution.java. On a workspace initialized before the playground existed, the first Run Playground creates the folder on the fly — no re-init needed.

Install

Requirements

• Python 3.10+ on your PATH (python3 --version must work). The bundled helper scripts use it to talk to LeetCode's API.
• pip install requests beautifulsoup4 — used by the bundled scripts.
• VS Code 1.85+.
• No local JDK required for Run/Submit — LeetCode compiles and runs your submission on their servers. A JDK (javac + java on your PATH) is only needed if you want to use the local playground/Playground.java scratch pad.

Then in a new folder run LeetKnight: Initialize Workspace from the Command Palette to seed .leetknight/reviews.json.

Safe to re-run on an existing workspace — init is idempotent. It creates only what's missing (.leetknight/reviews.json, playground/Playground.java, workspace README.md) and never overwrites your ratings, problem folders, or playground code.

LeetCode setup

Test/Submit hit LeetCode's authenticated endpoints, so LeetKnight needs your browser session cookies:

1. Log in to leetcode.com in your browser.
2. Open DevTools → Application → Cookies → https://leetcode.com.
3. Copy the values of LEETCODE_SESSION and csrftoken.
4. Run LeetKnight: Set LeetCode Cookies from the Command Palette and paste them (they're stored in VS Code's SecretStorage, backed by your OS keychain).

Cookies typically last ~2 weeks. When they expire you'll see an [auth] message telling you which one to refresh.

Daily workflow

1. Add a problem — LeetKnight: Search LeetCode (or New Problem from URL). Picks land at <workspace>/<slug>/ and the Solution.java auto-opens.
2. Iterate — click ▶ to run example cases. Fast, doesn't count as a submission, uses LeetCode's own judge.
3. Submit — click ☁️, confirm y in the terminal. On Accepted, a modal pops up: How hard was this? Pick Hard / Medium / Easy (dismissing defaults to Easy).
4. Practice later — open the LeetKnight activity-bar entry. Your solved problems are grouped by rating with hardest at the top. Click any row to re-solve — it opens the file and resets to the starter in one step. Or click the random-pick button for interview mode.
5. Reset manually — the ↻ button in the editor toolbar resets Solution.java back to the starter. Panel-click and random-pick do the same as part of opening the problem, so you don't need to reset separately.

Commands

How it works

• Every problem you scaffold gets a hidden <slug>/.leetknight.json cache containing the LeetCode questionId, exampleTestcases, and the original initialCode. This means Run / Submit / Reset don't need to re-hit LeetCode's rate-limited GraphQL endpoint on every invocation.
• Ratings and attempt history live in a single <workspace>/.leetknight/reviews.json — human-readable, git-committable, portable between machines. This is populated organically as you submit; there is no bulk history import.
• Communication between the Submit script and the VS Code extension happens via <workspace>/.leetknight/pending.json: the Python script writes it on Accepted, the extension tails it with a FileSystemWatcher, pops the rating modal, and deletes the file.
• Language is fixed to Java. Every problem is scaffolded from LeetCode's java code snippet, and Run/Submit send "lang": "java" to the judge.

License

MIT