Advent of Code 2024 Retro

Advent of Code AoC is an annual programming competition that releases daily coding puzzles throughout December. For the past four years, I’ve tackled these challenges from the West Coast, where the 9 PM PST release time perfectly suits my schedule. While I compete for points on the global leaderboard (with modest success), the real joy comes from the community around it. Through Stripe’s solution-sharing Slack group, and the active r/adventofcode community, discussing creative approaches to challenging problems adds an new dimension to my favorite pastime - solving puzzles.

This is a retrospective of the most recent (10th year anniversary) 2024 installment of the competition.

Stats

• total time spent - 17 hours 42 min
• fastest day - day 1 - 0:03:23
• slowest day - day 21 - 3:00:42
• best global rank - 112 (day 20 part 1)
• worst global rank - 3909 (day 3 part 1)
• average global rank - 1014. For comparison ‘23 - 1062, ‘22 - 1523, ‘21 - 1208.

I didn’t make the global leaderboard, compared to last year where I scored global points 3 times, but my rank average improved slightly, so I am calling it a success.

Problems

• hardest problem - Day 21: Keypad Conundrum - Took me whole 3 hours. Something about the recursive nature of the keypads kept throwing me off.
• most fun problem - Day 24: Crossed Wires - I haven’t taken an EE class before, so it was fun to learn about full adders on the fly.
• most annoying problem - Day 13: Claw Contraption - I was nerd snipped into solving linear Diophantine equations, which do have a nice closed form solution, for close to an hour before realizing that one can just solve over the reals and check whether the solution is an integer or not.

Thoughts

This year’s competition felt easier than previous years, though this might simply reflect my growing familiarity with AoC’s distinctive style. I’ve noticed several patterns that differentiate AoC puzzles from others:

1. Input analysis is crucial. Unlike many programming competitions, AoC provides the actual input upfront, encouraging solvers to look for specific patterns rather than developing completely general solutions.
2. The toolset is intentionally constrained. While path-finding algorithms and basic mathematics are common requirements, reaching for complex algorithms usually indicates you overcomplicated the solution.
3. Careful reading matters. There are often some extra conditions in the problem statement, so when stuck it is generally a good idea to reread the problem.

I had fewer misreads and basic typos than previous years, but most of my time was lost overcomplicating the non-trivial days solutions. For example, for Keypad Conundrum I had an initial solution with full enumeration of 16 expansion strategies (‘how to go from A to v’, etc) and hashmap counting each transition. The day after I learned that the problem can be solved much more cleanly with dynamic programming, so I simplified the solution down to this DP, nearly 5x shorter than my original code.

The AI question

A lot of the conversation this year revolved around the use of AI for solving problems. While the authors of the contest discourage direct AI usage here, they also admit that they can’t really stop anyone from doing so. Since its release, I have been using Github copilot for all coding including AoC. This would undoubtedly be perceived by some as cheating. In my defense, many people use AOC as exercise to learn a new programming language, and I am using it as an exercise to write code with AI autocompletions, which I do believe will be the future of all programming. I wouldn’t write a doc without a spellchecker, and I don’t see myself ever again coding without AI autocompletion.

That said I resisted pasting any of the problem statement or input into Claude, but don’t feel like I have a much of a higher ground over people who did. It is a wide and messy spectrum of x% human with 100-x% AI assisted, and everyone is picking a spot that works for them. Is 100% human even possible - can using pre-made specialized AOC libraries or compilers finding errors also seen as assistance? The fact that we reached a point what 100% AI is possible is wild, but it just one more spot on the AI spectrum and unless AOC want to define AI weight classes (like in sports) might be best to just take global ranking less seriously. Ultimately, solving the puzzle and reading all other solutions is the main part of the fun, and I view the global timing as just enough motivation to do the puzzles at a fixed time and with some urgency.

Speaking of Copilot assisted problem solving, it definitely has been somewhat of a learning curve on how to best collaborate with it on problem solving. I have gotten better at instinctively knowing where to just trust Copilot and where to double-check more. For example, a common mistake that copilot does is write grid[y][x] when I name my index variables x and y, that can often messes up my handwritten accesses that I write as grid[x][y].

With AOC problems often are of the shape of classic problem with a twist, and AI shines an just spitting out the classic solution inline, so I can edit in the twist. The traditional software engineering pattern would instead have me rely indirectly on a privates-protected external library and its extension interfaces that might or might not even allow me to add in the twist. With Copilot is making it so easy to generate large chunks of of code inline, I wonder if we will start to see a bigger shift away from code-reuse to code-regenerate.

A global phenomenon

I am really enjoying the fact that AOC has become somewhat of a big global phenomenon. Day 1 was completed by quarter million coders! As a puzzle connoisseur this feels like the time of the year where I can share my hobby with the most other people. There is something magical about so many brains focusing on the same problem for a few hours in the same day and submitting memes and solutions on r/adventofcode. I tried to contribute this year with the occasional upping the ante (day 3) post.

Future

I do plan to keep doing AOC annually as long as the timing commitments allow me, but I do wonder if it can continue to evolve in the next 10 years without becoming captured by the majority of the audience and become repetitive. There is already a tension between users that want more straight forward coding challenges and ones that prefer problems that push them to learn new algorithms or math concepts. Clearly, I am in the second camp, but I can relate to the frustration of having to learn a new concept on the fly, while competing to time with someone what just knows it already. AOC is starting to repeat the same handful types of problems - a 2d path finding problem with a twist, a classic graph algorithm, a memoized DP, or find the period in a repeating pattern, etc. Meanwhile, The world of CS and math knowledge is vast and I would love to see more areas appear in gamified in AOC.

To Eric, AoC’s creator (in case he ends up reading this) - Thank you for the first 10 years of AOC! I hope you continue to push the boundaries with what might be the biggest CS puzzle community and introduce us to new corners of computational thinking. We can handle the challenge.