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Advent of Code 2025: Number of puzzles reduce from 25 to 12 for the first time

https://adventofcode.com/2025/about#faq_num_days
81•vismit2000•2h ago

Comments

vismit2000•2h ago
From FAQ: "Why did the number of days per event change? It takes a ton of my free time every year to run Advent of Code, and building the puzzles accounts for the majority of that time. After keeping a consistent schedule for ten years(!), I needed a change. The puzzles still start on December 1st so that the day numbers make sense (Day 1 = Dec 1), and puzzles come out every day (ending mid-December)."
shrx•1h ago
One of the reasons I stopped participating was that as the second half of december was approaching I had less and less free time for solving the puzzles. So to me it is also a welcome change, I will try to finish it again this year.
seabombs•1h ago
Agree. It was getting in the way of me spending time with the family because I was distracted mulling over the puzzles.

I had thought last year that they could peak the difficulty around the middle of the month and bring it down a bit leading up to the 25th. But just finishing it earlier is probably better IMO.

jojobas•1h ago
Doesn't help that the puzzles become increasingly tricky and you can't just solve them as you sip your coffee anymore (although some apparently can).
NoboruWataya•58m ago
Same, I love AoC but I just never have time for them (December is always the busiest time of year in my job).

I would have liked if a puzzle was released every 2 days though so it still spanned the whole month. Would be more aligned with the advent calendar concept. In fact in previous years the puzzles have always had two parts so if that format is still being retained there will still effectively be 24 puzzles.

emerongi•27m ago
Spreading the two parts across separate days would be interesting. There would be an extra element of trying to predict what part 2 will be like.
rich_sasha•38m ago
I once has this half serious idea to do "Advent of Parenting", with one problem per month, and you start after Christmas. As in, youre so delayed you start in the New Year, and have time for one problem per month.

But hey I didn't have the time to do it. Kids...

thomascountz•1h ago
Whenever there's a change like this, my gut reaction is to grieve and try to imagine ways that things could be kept the same.

After thinking, "maybe puzzles could be designed by a group instead of an individual and they could share the work," I then thought, "and couldn't an LLM help?"

And with that, I had to remind myself: Advent of Code isn't about there being 25 puzzles, and so maintaining volume at all costs has nothing to do with it.

And aren't we so lucky that it isn't! Aren't we lucky to have had the prior 500+ challenges given as gifts over the years! Aren't we lucky to have a great demonstration of humility and care! Aren't we lucky to have 12 new gifts to look forward to this year!

Thank you!

petesergeant•1h ago
I’ve been trying to design a puzzle for a game this year that humans can solve but LLMs can’t. I’ve come up with one, but it was hard work! It’s based around message cracking.
ekimekim•1h ago
There was one in a previous AoC that I think stumped a lot of AI at the time because it involved something that was similar to poker with the same terminology but different rules. The AI couldn't help but fall into a "this is poker" trap and make a solution that follows the standard rules.
petesergeant•49m ago
Interesting! Maybe that’s the general way to approach these things
sunrunner•39m ago
Was that 2023's Day 7 'Camel Cards' [1]?

[1] https://adventofcode.com/2023/day/7

gf000•13m ago
I mean, wasn't pretty much the second half of all AoC exercises beyond LLM capabilities?

I remember there being multiple accounts trying to one-shot AoC and all ended on day 10 or so.

thaumasiotes•44m ago
> And with that, I had to remind myself: Advent of Code isn't about there being 25 puzzles

Really? The name of the event is "Advent of Code". Having 25 puzzles is easily its most strongly-determined aspect.

You could argue for 23-29 puzzles, or perhaps for 5, but at 12 what's the name supposed to refer to?

eterm•43m ago
Well advent calendars traditionally had 24 doors.
matrss•32m ago
IMO "Advent of Code" only determines the timeframe in which it happens, not the amount of puzzles it must contain. It could just as well be four puzzles, one for each sunday of the advent, or any other amount, as long as they are released within those roughly four weeks before christmas.
danielbln•6m ago
Eh, the implication has always been that it's a Christmas calendar where you open one door per day until it's Christmas eve - just with code riddles instead of chocolate.
akho•27m ago
Twelve nights of Christmas. Would also work better for me, calendar-wise :)
nikanj•1h ago
Tryhards ruin everything, part n

Make a fun little christmas calendar to bring joy to the people, get turned into a gamified warzone where people use AI and bots to try to get onto the global leaderboards - possibly because getting on them might net you a job at FAANG

iamflimflam1•54m ago
People - the reason why we can’t have good things.
fjfaase•46m ago
The temptation to start a competative private leader board will be great, just for the mentioned reason. I have a reference my scores in my CV. The competative part of AoC is one of the things that I find attractive and also has taught me some valuable lessons about coding, like taking some time to review the code the first time before submitting. I experienced several times that I spend of time to debug a small bug due to a minor error, that I could have caught had I spend some time reviewing. Especially with the first puzzles, I try to get it right the fitst time with respect to compiling and execution.

I will search for a pure C private group to join that only allows a small library for things like reading the input as an array of strings.

ozim•40m ago
Fun part is that world mostly doesn’t really work like that and they don’t really get the job.
lexicality•59m ago
I see the leaderboard is gone too. Unfortunate but entirely predictable given how the last 2 years went.

That being said, I was worried he'd cancel the entire thing, so this is still good news!

aronhegedus•57m ago
I've participated in the past, and felt like I always drop off around day 18+ because of holidays etc.

I personally also didn't like when part II of a question felt like a completely new question, instead of a neat extension of the previous one.

I am very happy that this is something that's available to do, for free though. I see advent of code as a good excuse to dabble with a new language, usually with a few people from work.

defanor•54m ago
On the bright side, this will lead to a more relaxed December schedule. I do not compete for the leaderboard, but trying to solve the puzzles on the days they are released (to keep it in the spirit of an advent calendar), and the puzzles towards the end sometimes take me a considerable chunk of the day to solve, which is tricky to combine with the regular schedule, and may be rather stressful (though still a nicer kind of "stressful", as you get on celebrated holidays).
sunrunner•25m ago
This matches my experience, and I've been 'nervously' anticipating this year's Advent of Code. I managed to keep to the spirit last year and get everything done by Christmas day (though admittedly with some days bleeding over into other days due to pesky family/other commitments), but even this relied on having the last week or so of the month be relatively free for me.

While I've usually been able to do the first half of the month's puzzles in the day before breakfast, over lunch and in the evening, the increasing difficulty does mean that later puzzles can really eat into a day, particularly if you happen to go down a bad path for your solution.

sunrunner•45m ago
I genuinely look forward to Advent of Code every year (whatever that says about me) and next year's one is always on my mind, so naturally I'm somewhat sad about this as the one-puzzle-a-day up to Christmas day just felt very neat, and I liked the mostly gentle initial difficulty curve up to the more 'spiky' questions later.

Having said that, having done a few years now I think the following things end up feeling consistent across years:

The first 10-ish (give or take) days were always simple enough that experienced programmers can likely spit them out during their daily standup. This isn't bad, as I think they're great for newer programmers to get a bit of algorithmic and data structure thinking practice, but they can definitely feel a bit same-y once you've done a few years. This isn't a critique of how AoC was structured, just an observation of how it can feel after you've seen a few years. Having said this, I'm sure I'll miss the gentle warm-up this year.

I wonder what this means for the difficulty curve i.e. the almost-inevitable path-finding question will appear on Day 5 and not Day 15?

I'm sure Eric has thought this through but I wonder if an every-other-day approach (perhaps with a 'softer' puzzle for Christmas day itself) would be popular, as I imagine people balancing a job and/or family while wanting to do this might appreciate having two days for the more challenging later puzzles.

On the other hand, free time for this generally does get more tight as you get closer to the end of the month and the puzzles get more challenging, so this approach does just make a chunk of space for people later in the month, and individuals can choose to keep up with the puzzles on release day if they can or just not worry about it and let things roll over.

Unfortunately, I guess I'll have to actually go and see my family this Christmas instead of ignoring the mandatory visits, which seemed like a fair sacrifice to keep up with calendar ;)

> It takes a ton of my free time every year to run Advent of Code, and building the puzzles accounts for the majority of that time. After keeping a consistent schedule for ten years(!), I needed a change.

Completely fair. As Eric says in some of his presentations on this it takes him about three or four months of his spare time, so this is more than understandable. Props to him for keeping this up consistently with his day job for the last ten years.

> The global leaderboard was one of the largest sources of stress for me, for the infrastructure, and for many users.

I don't mind this so much personally (outside of a morbid curiosity in the really fast participants) although I know people that were really invested in it, but there were some genuine points of contention for people that were interested in the leaderboard:

- The global puzzle unlock time, while explained by Eric himself in his presentations, does make being on the leaderboard impractical for people outside of time zones where the actual release time is friendly for that. For me it's 5am, and the only time I ever came even close (while also being nowhere near...) was when I happened to be up at that time due to insomnia (not caused by AoC).

- It sounded like an infrastructural point of pain as the single global release time coupled with submissions-by-country-size and how keen some of the puzzle solvers are makes for a great initial traffic burst with a long tail (also mentioned on the behind-the-scenes videos).

- It naturally favoured people with an interest in these kinds of puzzles, so the selection bias in the leaderboard is inherently skewed towards a) the subset of people that are choosing to do this out of genuine personal interest and then b) the subset of those that are likely to also be interested in competitive programming-type challenges. This is natural, but I think it does make the leaderboard less relevant for the majority of participants.

- The inevitable contention of the use of 'AI' just to be on the leaderboard

Anyway, I'll just end this with a thank-you to Eric himself for designing and running this consistently for the last ten years as it's something I've come to really enjoy, the community is very lucky to have this, and I hope these changes make it possible for him to continue doing this with lower physical costs to him personally and perhaps lower stress for the participants that just enjoy the puzzles for learning and the rare opportunity to write simple programs to solve problems.

For interested watchers:

- 'Eric Wastl – Advent of Code: Behind the Scenes' - https://www.youtube.com/watch?v=_oNOTknRTSU

- 'Keynote: Advent of Code, Behind the Scenes - Eric Wastl' - https://www.youtube.com/watch?v=uZ8DcbhojOw

Edit: Typos

cod1r•43m ago
This is sort of a bummer but as long as Eric feels less stressed and more happy, I'm all for it.
kykat•38m ago
why not a puzzle every two days instead of ending it mid-december?
exegete•3m ago
You will have that option
HiPhish•8m ago
If he has cut the number of puzzles in half, why not then release a new puzzle every other day? That would make more sense because AoC would still run until Christmas, and it would give people more time per puzzle. Maybe unlock part 2 of each puzzle the day after the puzzle has been posted, so there still something new every day.

I once tried participating, but gave up halfway through because one puzzle per day was just too much time. If it was one puzzle every two days it would be more manageable.

akerl_•6m ago
If they’re released every day for 12 days, you can do a puzzle every other day.

If the were released every other day, people who wanted to do them for 12 straight days could not.

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