Advent of Code 2025 Day 12 (BaseA Style)

AlteryxCommunityTeam

Discussion thread for day 12 of the Advent of Code - https://adventofcode.com/2025/day/12

Advent of Code

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ScottLewis

Happy Advent, Everyone.

Cannot stress the spoiler part of this one enough.

Spoiler

A lesson in floors and ceilings.
Often, while you can't see the answer from looking at a problem, you can bound that problem with a floor or a ceiling.
This is important because it can define the possibility space you have to search and allow you to discard possible designs that search too much of the space.
In this case, the ceiling is "How many of these trees could fit all the presents if they were packed perfectly."
A lot of them can't.
From there, you could reasonable determine an optimal packing of one of each shape and take out min (count of shapes) from the space, testing only the possible trees and that would possibly eliminate a few more.
Unless the packing was perfect, which it appears to be, in which case the ceiling is the answer.

Part 2, is, of course, not to be spoken of until you have the rest of your stars.

Final

Spoiler

AOCDay12ScottLewis.yxmd

CoG

Echoing @ScottLewis , DO NOT check spoilers unless you want this entire day solved with a single glance. It's not as hard as it looks and feels quite good to solve if you can get it. If you're struggling to wrap your mind around this problem, try to think about simple steps you can take, and see what's left after you do that. If you've tried and you're still stumped, then continue reading!

Spoiler

With every complex problem, it can help to remove the obvious that would simply get in the way as clutter so that you can invest your focus, effort, and computational time, where it really matters. In this case there are two such obvious cases that you can attend to:

1. If you were somehow able to pack these gifts absolutely perfectly with no gaps that could be filled, how much space would they take up? In my problem there was one piece with a 2-unit deep pit, the center of which was unreachable by any piece, so that can be counted as part of the gift size for that gift.
2. If the area you are working in is sufficiently large, then you could just lay each gift next to the other without any interlocking at all.

In case one, none of those regions would fit the presents, and case two all of those regions would fit the presents quite easily. The best part! All of the regions fit into one of the two categories. So Filter off Case 1 regions and you are done!

I enjoyed solving with y'all this year! Thanks for all your efforts and encouragement. Y'all are a blast to work with! Here's to next year!!! So glad I was able to finish Day 10 just before Day 12 released.

Happy Solving!

Workflow.yxmd

Gawa

Spoiler

My advice is "Don't try rigorous approach."

2025D12_gawa.yxzp

Hub119

Like @ScottLewis and @CoG mentioned this one turned out to be much simpler than I thought it would be...

Spoiler

I started by building out a simple test to see what plots could even be remotely possible for this to work based on overall available plot area, number of presents of a given type needed, and number of spaces each would take up (assuming a perfect arrangement where they all interlock perfectly). With the potential viable test cases prepped I was ready to go further (see next spoiler for 🤣). Based on a "don't overcomplicate this" comment from @CoG I decided to just try throwing my existing viable plots to test count in as a solution... what do you know? It worked.
AoC 2025 D12 Pic.png

Spoiler

Shape rotation and flipping assembly prep copy/pasted from AoC 2020 Day 20 Solve

AoC 2025 Day 12 - Christmas Tree Farm.yxzp

Qiu

In the spirit of keeping it simple...
Can not believe the AoC of the year has completed and I have gotten my first Tree.

Thank you all for the jouney together and the wisdom you have shared.
Happy Upcoming Holidays and wish you all continue to be awesome for the comming year! ❤️

Spoiler

AoC 2025 Day 12-Qiu.yxzp

DaisukeTsuchiya

Experts told me not to overthink Day12.

Spoiler

I tried an approach that I thought might work. It didn't pass the sample cases, so I gave up and asked @gawa
for a hint. He told me that while my logic wouldn't work for the sample cases, it would work for the actual problem. I tried it, and it worked!

スクリーンショット 2025-12-12 162330.jpg

DT2025_Day12_Rev0.yxmd

Goddenra

Thoroughly enjoyed this year's competition! Thanks for all the great insights, it's been fascinating to learn some new tools and see how other people tackle problems.

Spoiler

I too listened to the experts and, I don't know, it seems a little easier to get the right answer for Part 1 than it should be. Saying that, I'm not entirely sure how I'd solve it in the way I think it should be.

No spoilers for Part 2 though I'm afraid. The code does not allow such things.

Day 12.yxmd

DanFlint

Spoiler

Probably too much rearranging the data into the right layout.
Then (at everyones suggestion) tried the easy thing first

Day12DF.yxmd

DataNath

Day 12 done! Had a bunch of fun this year. As someone who falls apart with the more complex challenges due to a lack of mathematical ability or CompSci background, I've appreciated them not being too extreme (with the exception of Day 10 of course)! I think I'll be able to give Part 1 of that a crack but Part 2 seems completely out of reach from what I've heard - this blocks my 24th star as well as that's given upon Day 12 completion and having all stars up to that point. Happy advent all, it's been a blast again!

Don't read the spoiler unless you instantly want the method...

Spoiler

It turns out there's no need to do any rotating and checking - the actual data set all fits perfectly so it's literally just a check of 'does the area of presents required exceed the area of the tree'?

Day 12 - Cleansed.yxmd

mmontgomery

Day 12

Spoiler

I tried to build something fancy using spatial, and after an hour or so, I checked the community to see if I was on the right path - and nope! Turns out the problem structure makes it seem way harder than it is. Once I saw those hints, thanks @CoG and @gawa, I just did some simple math and got the right answer.

Day12.yxzp

AkimasaKajitani

I think that this is a narrative trick...or the best problem to fool AI.

Spoiler

Thank you to everyone who participated in this year's Advent of Code. The number of problems this year was a little disappointing, but it was still fun. I look forward to seeing you again next year! And Happy Christmas and new year!

Day12.yxzp

Pilsner

AOC 2025 COMPLETE! Saw some of the comments for this one saying "don't overcomplicate it". Spent about an hour dragging a couple of tools on, then deleting them again, before I decided to just try something simple to start. Turns out that was the answer, if only I'd listened to the comments 😂

Overall, a great end to a very enjoyable AoC, I've learnt so much from others' solutions, so thank you all, and a big congratulations to all participants! Final shameless shoutout to Euleryx for anyone looking to continue the nerdy chatter and "mathsy" problem-solving into the new year.

Happy Christmas 🎄

Spoiler

I am a couple of days behind in my uploads, so I will be getting the remaining published shortly, but in the meantime, here is my workflow for day 12.

Workflow:

Part 1

1) To begin with, I created a group ID. This was based on line breaks, so every time there was a line break, the group ID increased by 1. This helped to label the 6 presents 0-5, and also mark the grid inputs as group 6. I proceeded to filter the group 6 items out, so I could deal with them separately.

2) Looking at just the grids, I then decided I need to separate the present counts from the grid dimensions.

3) With the dimensions isolated, I now needed to list the counts of each present per line, so I could actually do something with them. The important thing here is to then ID these lines, so that I can later join them up to their corresponding present.

4) Now, going back to step one, on the false anchor of the filter, I have all my puzzles. All I wanted to do, was count the number of spaces they each occupy. I did this by counting the number of # per line:

Then summing that count, per present (group) ID:

5) Now to join these counts to the corresponding present ID from step 4.

6) With both the number of presents needed per grid, and the count of spaces each present occupied now side by side, I was able to multiply these two values together to get the total number of spaces occupied per grid per present ID. Summing these values per grid then gave me the total spaces occupied per grid.

7) But, does each grid contain enough space to satisfy, the requirement? This is effectively he final check. I used regex to help me extract and then multiply the grid dimensions before filtering to make sure the total grid area was greater then the spaces required.

Day 12.yxzp

Stosh

Day 12 definitely left me with a smile on my face, for sure😅 And with that, the Alteryx Base-A AOC Challenge is complete!

My Solutions:

Spoiler

Part 1 (and Part 2😉) solution

My Reflection:

Spoiler

In terms of problem description, this was easily the most intimidating puzzle in the challenge. I promised myself I wouldn't stay up all night in order to solve it, but I was awake at midnight so I decided to just read the problem and WOW! I almost couldn't fall asleep for a bit there out of sheer confusion and nervousness for how I would solve this. I went to bed with questions and woke up with more, but I knew the best thing was to just start it up and see what happens. After all, I came way too far to give up now! I decided to just try to identify as many 'obvious' cases as possible from the pool of tests before being forced to come up with some way to rotate shapes🤣. I identified two ways to identify if a test could be immediately considered pass or fail: If the sum of the sizes of all the required gifts exceeds the size of the grid, the test is a guaranteed fail, as no rotations or alignment can make up for a lack of space. Conversely, since all gifts are 3x3 in square dimension, if a grid has enough 3x3 sub-grids to house the full count of required gifts, then it is an automatic pass, as rotating and stacking gifts is no longer relevant or required. As I was configuring these tests, I was hoping and praying that these tests would thin down the list considerably and then it happened: The Christmas miracle! As it turns out, all 1000 cases fall into one of these two categories, and the problem is solved! This was a cool case of handling your upper and lower bounds before being bogged down with the intricate cases, and I am so glad that I approached it exactly how I did.

Overall, my first Alteryx AOC has been an incredible experience. I learned so many cool Alteryx concepts, was introduced to new to new tools, and met so many cool people! I want to give a shout out to @OllieClarke for introducing me to this challenge and to all the other folks in the group-chat, whose help was utterly indispensable in each and every challenge. By next December, I hope to have a lot more stars under my belt from previous AOC challenges and will be shooting for the leaderboards. Looking forward to seeing you guys in the Weekly Challenge discussions!

AOC2025.12.yxmd

AncientPandaman

done.

Spoiler

Day 12.yxmd

Tokimatsu

Solved.

Spoiler

I thought I couldn't solve this problem, but when I eliminated the answers I was sure were wrong, the solution came to me.
スクリーンショット 2025-12-24 140037.png

AoC2025Day12_toki.yxzp

OllieClarke

Sometimes simple is best

Spoiler

Now to go back to Day 10

Day 12.yxmd

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