Crédit:
The Advent of Code is a set of daily programming challenges proposed by E. Wastl during the month of December.
All information here: adventofcode.com
Disclaimer: all the images in this post are AI-generated based on the day story.
For the technical breakdown and code solutions for each day, check out the Advent of Code 2025 Recap.
Cosy Variant
Sci-fi Alone
Sci-fi Together
The Full Story
The Elves have good news and bad news.
The good news is that they've discovered project management! This has given them the tools they need to prevent their usual Christmas emergency. For example, they now know that the North Pole decorations need to be finished soon so that other critical tasks can start on time. The bad news is that they've realized they have a different emergency: according to their resource planning, none of them have any time left to decorate the North Pole!
To save Christmas, the Elves need you to finish decorating the North Pole by December 12th.
Day 1: Secret Entrance
You arrive at the secret entrance to the North Pole base ready to start decorating. Unfortunately, the password seems to have been changed, so you can't get in. A document taped to the wall helpfully explains: "Due to new security protocols, the password is locked in the safe below."
The safe has a dial with only an arrow on it; around the dial are the numbers 0 through 99 in order. As you turn the dial, it makes a small click noise as it reaches each number. You're sure that's the right password, but the door won't open. You knock, but nobody answers. You build a snowman while you think.
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 2: Gift Shop
You get inside and take the elevator to its only other stop: the gift shop. "Thank you for visiting the North Pole!" gleefully exclaims a nearby sign. You aren't sure who is even allowed to visit the North Pole, but you know you can access the lobby through here.
As you make your way through the surprisingly extensive selection, one of the clerks recognizes you and asks for your help. As it turns out, one of the younger Elves was playing on a gift shop computer and managed to add a whole bunch of invalid product IDs to their gift shop database!
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 3: Lobby
You descend a short staircase, enter the surprisingly vast lobby, and are quickly cleared by the security checkpoint. When you get to the main elevators, however, you discover that each one has a red light above it: they're all offline.
"Sorry about that," an Elf apologizes as she tinkers with a nearby control panel. "Some kind of electrical surge seems to have fried them. I'll try to get them online soon." The escalator also needs power. Maybe you can get it running while she keeps working on the elevators.
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 4: Printing Department
You ride the escalator down to the printing department. They're clearly getting ready for Christmas; they have lots of large rolls of paper everywhere, and there's even a massive printer in the corner.
"Actually, maybe we can help with that," one of the Elves replies when you ask for help. "We're pretty sure there's a cafeteria on the other side of the back wall. If we could break through the wall, you'd be able to keep moving. It's too bad all of our forklifts are so busy moving those big rolls of paper around."
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 5: Cafeteria
As the forklifts break through the wall, the Elves are delighted to discover that there was a cafeteria on the other side after all. You can hear a commotion coming from the kitchen. "At this rate, we won't have any time left to put the wreaths up in the dining hall!"
"If only we hadn't switched to the new inventory management system right before Christmas!" another Elf exclaims. Because of their complicated new system, they can't figure out which of their ingredients are fresh and which are spoiled.
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 6: Trash Compactor
After helping the Elves in the kitchen, you were taking a break and helping them re-enact a movie scene when you over-enthusiastically jumped into the garbage chute!
A brief fall later, you find yourself in a garbage smasher. Unfortunately, the door's been magnetically sealed. While you're trying to figure out how to escape, you are approached by a family of cephalopods! They're pretty sure they can get the door open, but it will take some time. While you wait, the youngest cephalopod asks for your help with their math assignment.
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 7: Teleporter Hub
After thanking your cephalopod friends, you escape the trash compactor and find yourself in the familiar halls of a North Pole research wing. You discover a facility labeled "teleporter hub" and step onto a large yellow teleporter pad.
You're transported to an unfamiliar room! The room has no doors; the only way out is the teleporter. Unfortunately, the teleporter seems to be leaking magic smoke. Using the diagnostic equipment, you identify error code 0H-N0, indicating an issue with one of the tachyon manifolds.
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 8: Playground
The teleporter brings you to an underground space containing a giant playground. A group of Elves are constructing an elaborate Christmas decoration project involving suspended electrical junction boxes.
The Elves need to connect these junction boxes with strings of lights so that electricity can reach every location. But they have limited materials: "To save on string lights, the Elves would like to focus on connecting pairs of junction boxes that are as close together as possible."
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 9: Movie Theater
You slide down a firepole in a corner of the playground and arrive at the North Pole base movie theater!
The Elves are redecorating the theater by replacing tiles in a grid floor pattern. Some tiles are red, and the Elves need to identify the largest possible rectangle using red tiles as opposite corners.
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 10: Factory
You arrive at a large factory where the Elves are unable to operate the machines: "the factory machines are all offline, and none of the Elves can figure out the initialization procedure."
The comedic twist: the instruction manual's section detailing the initialization procedure was eaten by a Shiba Inu! What remains are only partial technical documents - indicator light diagrams, button schematics, and power specifications.
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 11: Reactor
You hear loud beeping coming from a hatch in the floor of the factory. Descending the ladder, you discover a large toroidal reactor powering the facility above.
An Elf urgently explains: "We just installed a new server rack, but we aren't having any luck getting the reactor to communicate with it!" The team believes the issue is triggered by data following some specific path through the devices.
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
Day 12: Christmas Trees
Racing against time, you discover a ventilation duct that leads to a large, well-lit cavern full of Christmas trees. A group of Elves are working frantically to decorate before the deadline.
They face one significant worry: "the presents for all the young Elves that live here at the North Pole." It's an ancient tradition to put the presents under the trees, but the Elves are worried they won't fit. The presents come in various unusual shapes and must be placed on a two-dimensional grid - they can be rotated and flipped, but cannot overlap or stack.
↑ Images: Cosy | Sci-fi Alone | Sci-fi Together
And with that, the North Pole is decorated just in time for Christmas!
For the technical breakdown and code solutions for each day, check out the Advent of Code 2025 Recap.