[KatalKavya96]

Requested by Kavya Katal · project thread

Problem or area changed

Visual Lab (dist/): adds a code runner so readers can try a problem on the spot. You get an editor, a custom stdin box, Run/Stop and output. There are no test cases and no judging, by design.

• New Compiler view at #compiler (linked from the top nav).
• Every solution book gets a Try it yourself page right after "Build the approach", before the code pages. That way readers attempt it before they read the solution.
• An optional catalog field problemUrl adds a "Read the full statement on LeetCode ↗" link on the first page and on the practice page. Statements are linked, not copied. It's filled in for 4084 and 4085 from metadata.yaml.
• Drafts, input and language are saved in localStorage, separately for each problem.

The insight

The site is public and static (GitHub Pages / Vercel), so everything runs in the reader's browser. There's no execution server to host, pay for, or get abused, and code never leaves the device.

• Python: Pyodide 314.0.7 (CPython 3.14) in a module Web Worker (dist/python-worker.mjs), loaded from jsDelivr. The 10 s time limit and the 100k-character output cap work by terminating the worker. Tracebacks are trimmed to the reader's own main.py frames.
• Java 17: CheerpJ 5.0. javac compiles the reader's file plus a small PgRunner class that points System.in at the input box and calls main(). CheerpJ is free for personal and educational use.
• The editor is a plain textarea with a line-number gutter, Tab/Shift-Tab indent, auto-indent after : and {, and Ctrl/⌘+Enter to run. Escape followed by Tab leaves the editor. No new dependencies and no build step.
• Asset cache keys go from solution-book-1 to compiler-1.

Verification

• python3 scripts/validate_repo.py: all checks pass.
• Playwright (Chromium) against python3 -m http.server --directory dist, with the Pyodide files served from the npm package because this sandbox can't reach jsDelivr:
  • Default template prints 15.
  • A runtime error shows a clean traceback.
  • while True: pass stops at 10 s, and the next run restarts Python and works.
  • A print flood stops at the output cap.
  • Typing checks auto-indent and smart backspace. Ctrl+Enter runs.
  • Arrow keys inside the editor don't turn book pages.
  • Language choice persists across reloads.
  • No horizontal scroll at 390 px.
• Not verified: the Java path end to end. The sandbox blocks CheerpJ's CDN (cjrtnc.leaningtech.com). I checked the PgRunner wrapper and the Java template with a local JDK 21. The javac-in-CheerpJ approach follows Leaning Technologies' JavaFiddle. Please try Java once on the Vercel preview.

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Generated by Claude Code

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Project	Deployment	Actions	Updated
katalkavya96_cp	Ready	Preview	Nov 4, 2026 4:57am UTC