LeetCode's contest page has an "Add to Calendar" button for adding a contest to Google Calendar. But it is for a single contest and is not subscribable.

So I wrote a script to automatically generate iCal file for weekly contests: https://github.com/gowee/lccal-worker/ .
It is now deployed here: https://lccal-worker.bamboo.workers.dev/ical.

It is generated every a few moments and hence always up-to-date. By subscribing to it, such as via Google Calendar: https://calendar.google.com/calendar/r/settings/addbyurl or Outlook: https://outlook.live.com/calendar/0/addcalendar - "Subsribe from web", new contests will appears in the calendar automatically.

Suggestions (or stars) are welcome :P