As a world's leading online programming learning platform, LeetCode is quite popular among programmers. Since each problem has a unique number id, users tend to share problems via id. However, it is not convenient to visit problem page directly via id. People have to visit LeetCode Problems firstly, then enter that number id in the 'Search questions' input box, press 'enter', click the problem title link, finally comes to the problem page. What a hard work!

This simple project, called LCid, provides directly access to LeetCode problems via id. Features:

• Fetch all LeetCode problems via crawler.
• Redirect to LeetCode problem page with problem id in the URL path via backend.
• Support both LeetCode global site and China site redirect.
• CI/CD, fetch all LeetCode problems daily and commit back to repository via GitHub Actions, then trigger backend rebuild and redeploy with the latest problems via Heroku.

LCid is now available at lcid.cc. Just add /<problem-id> at the end of lcid.cc (e.g. lcid.cc/1), then browser will redirect you to the problem page. Simple, fast, and make your live easier.

What's more, to redirect to China site, add /cn/<problem-id> instead (e.g. lcid.cc/cn/1). Interested in the brief info of the problem? Try /info/<problem-id> (e.g. lcid.cc/info/1) and find more!

To start LCid on your local machine, you should have python 3.7+ installed.

The crawler is implemented with urllib3 and backend is powered with flask.

To install all those dependencies, execute pip install -r requirements.

The frontend is built with React.js with Ant Design UI.

To build frontend, you should have Node.js 16.13.2+ with npm 8.1.2+ installed.

(older versions may work but not tested)

Updated Oct 29 2023, leetcode.com now protected with Cloudflare. To send request to any page or endpoint under leetcode.com, cf_clearance and csrftoken are required.

For now, it is difficult to automate way to get both cf_clearance and csrftoken. Therefore, it is okay to manually get from browser for now.

Once we fetched cf_clearance and csrftoken from browser, copy file .env to .env.local, fill both fields accordingly.

REACT_APP_BACKEND_API_URL="http://localhost:1437"
LC_CF_CLEARANCE="{manually get from browser}"
LC_CSRFTOKEN="{manually get from browser}"

To fetch all problems, execute python fetch_problems_all.py. Then, you will see the logs below.

Now try get csrftoken...
Got csrftoken fakecsrftokenfakecsrftokenfakecsrftokenfakecsrftokenfakecsrftoke.
Found 2060 problems in total.
Now try fetch all 2060 LeetCode problems...
All 2060 problems fetched.
All 2060 problems info saved into problems_all.json file.

After few seconds, all problems info have been saved into problems_all.json file in json format.

To start frontend, install all dependencies via npm install first. Then, start frontend development server via npm run start. By default, the development server will starts at http://localhost:3000.

To build frontend, use npm run build. The built frontend will be created at build/.

To start backend service, execute python app.py <port> (e.g. python app.py 1437). Then, the backend server will start at localhost:<port>.

Now you can try the following endpoints. All of them should work correctly.

• localhost:<port>/
• localhost:<port>/1
• localhost:<port>/cn/1
• localhost:<port>/info/1

To deploy the system for public access, of course, you can use any platform you like. Here, I use GitHub Actions and Heroku.

• GitHub Actions is used to fetch all LeetCode problems daily (execute python fetch_problems_all.py, get the latest problems_all.json) and commit back to repository. You would know how it works by analysing this config file.
  • Don't forget to set required sensitive environment variables in GitHub Secrets (settings/secrets/actions).
• Heroku would rebuild and redeploy the backend service once main branch of this repository changed. This can be configured at Deploy - Automatic deploys in your Heroku app dashboard.
• Heroku also support add additional domains to visit app. Here is the official guide.

• This is just a naive tool for convenient access and only call LeetCode API at low frequency. It only obtains public accessible data (no personal info or paid content collected and distributed). DO NOT ABUSE LEETCODE API!!!
• GitHub Repo: bunnyxt/lcid
• Author: bunnyxt
• License: MIT