Originally from [caird coinheringaahing's idea](https://codegolf.meta.stackexchange.com/questions/24021/advent-of-code-golf), I thought about how we could do it this year with such a short time before December, and I decided to gather some ideas from previous AoC events. (There's an [explicit permission](https://twitter.com/ericwastl/status/699455417768923137) from Eric Wastl, the one who runs the AoC event.)

As I found 25 potentially good challenge ideas from previous AoC events (2015-2020), **I'm running the Advent of Code Golf (AoCG) this year.** On each day between Dec 1st and Dec 25th (inclusive), a new challenge will be posted at UTC midnight. It is a free-for-all and just-have-fun-by-participation event, no leaderboards and no prizes for solving them fast or solving them in the shortest code. But, if the event goes well, I will hand out a few bounties to the *most active participants*, based on various measures.

For the **posting schedule**: I expect myself to be unavailable on weekends, and I might have problems on other days too. I'll post the challenges when I can at around UTC midnight, but if a new challenge doesn't go live for an hour, or on weekends, anyone else is free to move that day's challenge to main instead. Please **don't** post it as Community Wiki though (it causes all answers to be CW too). You can take some extra rep as a bonus for helping me run the event :D

## Event challenges

* https://codegolf.stackexchange.com/q/237856/78410
* https://codegolf.stackexchange.com/q/237920/78410
* https://codegolf.stackexchange.com/q/237995/78850 (Posted thanks to @lyxal)
* https://codegolf.stackexchange.com/q/238052/78850 (Posted thanks to @lyxal)
* [AoCG2021 Day 5: Balancing sleigh with lots of trunks](https://codegolf.stackexchange.com/q/238073/9288) (Posted thanks to @alephalpha)
* https://codegolf.stackexchange.com/q/238111/78410
* https://codegolf.stackexchange.com/q/238158/78410
* https://codegolf.stackexchange.com/q/238209/78410 (Challenge contributed by @Wheat Wizard (Grain Ghost))
* https://codegolf.stackexchange.com/q/238258/78410
* https://codegolf.stackexchange.com/q/238301/78410
* https://codegolf.stackexchange.com/q/238353/78850 (posted by @lyxal)
* https://codegolf.stackexchange.com/q/238400/78850 (also posted by @lyxal)
* https://codegolf.stackexchange.com/q/238448/78410
* https://codegolf.stackexchange.com/q/238492/78410
* https://codegolf.stackexchange.com/q/238522/78410 (Challenge contributed by @Wheat Wizard (Grain Ghost))

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This post serves as the announcement of AoCG 2021, but it is also a public sandbox of challenges that will be used for the event. I will write up the 25 challenges for feedback here. If you have another idea (specifically related to previous AoC problems), feel free to post it; we will refine it together and line up the posting schedule accordingly, in case we have to throw away some existing ideas.

Note to those who are opposed to the AoCG being AoC-G instead of Ao-CG: I don't have any intention to make the event an AoC-G. I simply saw AoC as a good source of challenges to *quickly* draw ideas from (I'd totally agree with using sandbox gems if we had much more time than ~2 weeks before December), and the majority of challenges will be quite different from what you see on the AoC.