Advent of code 2024 in Haskell

2025-07-24 - I sharpened my Haskell skills again this year
Tag: haskell

Introduction

I participated in advent of code 2024 in Haskell: it was a fun experience as always! Why writing about this now? Because I just finished the last puzzle!

I did the first 12 puzzles each day last December but then life happened and I could no longer complete one puzzle per day. I only finished the first 19 puzzles by Christmas then took the usual long break. I picked up this challenge again about a month ago while waiting at the airport and have now completed the last one.

Haskell for puzzles

Usually this kind of article is an opportunity to explain some of the patterns I used and things I learned. Solving these puzzles was a lot of fun as always.

The puzzles were interesting, my favorite one being day 24 in which you need to debug a binary adder. It is made of logic gates with a few wires that have been inverted and need to be fixed. It was the hardest challenge for me by far and I only solved it when I realized that instead of needing to simulate wire permutations I could try to build the adder from the pool of logic gates that were available. When I could not find a gate I needed, it meant I had to look for a wire to swap.

I also thoroughly enjoyed day 21 where you need to input codes via proxy robots and need to compute a very convoluted shortest path algorithm where the key was careful usage of memoization.

I will also make a special mention for day 13 where the problem can be reduced to a system of linear equations. I love an excuse to whip out a matrix triangularization to achieve this, but I doubly loved that I could use the Rational type to deal with exact ratio numbers computations. Haskell really shines in these situations!

Conclusion

I recommend tackling this kind of challenge, it is good to maintain or develop proficiency in a programming language. I love Haskell, I wish I could use it daily and not just for seasonal puzzles.