Advent of Code 2025: Waking Up With Puzzles

Source: Dev.to

Why I Do Advent of Code

Advent of Code has become a yearly thing for me. It’s a way to keep my algorithmic and data‑structure skills sharp, and something I look forward to every December. Over the years I’ve used it to learn new programming languages—I’ve done editions in Elixir, Java, TypeScript, and others. In the last few years, including this one, I’ve stuck with Python.

Another important part of Advent of Code for me is the community: sharing solutions with coworkers, posting about them on social media, and seeing how others tackled the puzzles. That interaction is often the most fun aspect of the whole event.

My Rule

I always try to get as far as possible, but I have one rule: I should be able to solve the puzzle on the day it’s released. From experience, letting a puzzle linger can let it take over too much time and, in the worst case, start to dominate my life. This year’s format—only twelve days instead of the usual twenty‑five—provided breathing room in December once the puzzles were done.

Morning Routine

My mornings during Advent of Code follow a pretty fixed routine. The puzzles unlock at 6 AM local time for me, giving me about an hour and a half before I need to go to work. I often say Advent of Code is the best alarm clock in the morning. Solving a puzzle wakes you up quickly and fits nicely into my coffee routine. At the same time, the event can eat into my sleep now and then, which is another reason the shorter format worked well for me this year. Fortunately, we had one weekend (days 6 and 7) where I could catch up on sleep.

Writing Blog Posts

This year I wrote a blog post for each day. Writing about the puzzles added a lot to my understanding of them—before I can explain a solution in writing, I really need to understand it myself. Teaching and explaining forces you to learn as well. While writing the posts, I struggled with deciding what to include: the full puzzle story or just the core algorithmic idea? In the end, the posts landed somewhere in the middle, with a bit of both.

Challenging Days

Some days were quite hard. Day 9, where shapes had to fit into each other, and Day 10, which involved integer programming—something I hadn’t implemented before—definitely stood out. That’s what Advent of Code is really about: learning new things by implementing them. On those harder days I switched to existing libraries instead of writing everything from scratch. I don’t mind that; as a software developer I use libraries all the time, as long as I understand what happens and the general steps of the algorithm.

AI Assistance

I also consciously added AI to the mix, mainly the GitHub Copilot integration in VS Code. I wanted to see how much I could code in collaboration with AI, using it to suggest libraries or write small helper functions. The most important rule for me was that I needed to understand all the code that was generated. Used that way, AI felt less like a shortcut and more like a tool to think with—a developer you can talk to and discuss problems with.

Lighter Days

There were also days that felt lighter. Day 11, for example, was a relatively clean and simple graph problem, and I arrived at a solution fairly quickly. Knowing how much I struggled with those kinds of problems in the past, moments like that make it clear where I came from and how much more comfortable these problems feel now.

Reflections

Looking back at Advent of Code 2025 as a whole, it confirmed a lot of things for me:

• Explaining things is still a big part of how I learn.
• I’m fine using tools and libraries when that makes sense.
• Clear boundaries—like a shorter event and solving puzzles on the day itself—help keep Advent of Code fun instead of overwhelming.

Most of all, I still enjoy waking up early in December to solve a puzzle. That’s probably the best reason to keep coming back, year after year.