Last year I did "Advent of Elixir" at my company with the puzzles from AoC. It was slow paced but I got some people excited about Elixir! I also followed José Valim on Twitch to see how he tackled those.

If you want to stay competitive, you've got to invest some time right before Christmas, so I gave up on that pretty quickly. Instead I did the puzzles at my on pace and spent some extra time playing with the puzzles that I found especially fun:

https://twitter.com/StefanChrobot/status/1080574491535781899

https://twitter.com/StefanChrobot/status/1078448111041892352

As a bonus, you get something to show whenever you're asked to share some code when applying for a job!

And then there's the learning factor - the puzzles are progressively more difficult, but I guess still doable for the average programmer. At some point some of them start to feel repetitive, but that's great if you get a good hold on processing data in your language of choice.