Even though I am participating for fun instead of taking these competitions too seriously, it is nice to have them checked in here esp. if I learn something new from them.
Funny little tasks with A and B parts for each day of December. I heard about this from code_report videos and the Russ Cox's video series using Ivy. There is no time pressure, so I can play with stuff I never have time for!
This is organized really professionally. There are around 6 rounds and some practice rounds over the year. The 4 tasks over 3 hours give a great opportunity to focus on algorithms and datastructures. The submission and judging system is great! I always enjoy when the test-suite points out some flow automatically. This is even available in practice mode after the competition, so I can practice afterwards. There are also official write-ups after the deadline so that is also a great way to learn something new.
It is pretty amazing what Google put together for free. But attending all rounds is hard, because they distribute the rounds so that every timezone has a fair chance! (My first ever round was on a Sunday at 5a.m. after a wedding :D)