Advent of Code 2024 - Index

Ongoing commentary of my Advent of Code 2024 puzzle-solving. Code with my solutions on Gitlab.

Daily-ish commentary

• Day 1-3: understanding what’s going on
• Day 4-5: grids and patterns
• Day 6: pathfinding and loopfinding
• Day 7: brute-force arithmetics
• Day 8: vector maths!
• Day 9-10: a frustrating day, a satisfying day
• Day 11: oh no.
• Day 12: borders, connections and gaps.
• Day 13: into the matrix.
• Day 14: robots and a Christmas tree.
• Day 15: robots and boxes, thin and wide.
• Day 16: into the maze.
• Day 17: 3-bits computer.
• Day 18: back into the maze, but now it moves.
• Day 19: combining (too many) patterns.

What is this?

Advent of Code is an advent calendar of coding puzzles. Every day, Eric Wastl puts up a two-part puzzle, and we get to try to solve it. There is a cute Christmassy story line, and it’s all very geeky and fun.

I’m writing up my solutions here, mostly as a way to document my thoughts process in solving these kind of things and highlighting some things I learned or relearned along the way.

The rules

There are no rules to the challenge itself. There’s just a box to put the solution (always, until now at least, an integer number) of the first part, then it unlocks the second part, for which there is another answer box.

All puzzles follow the same structure: you have some example data used to explain the rules of the puzzle, then you can download the real data that you need to use for getting the solution. The data is always presented in pure text, which you have to parse into a useful data structure – that’s always the first part of the puzzle.

My rules

Everyone who participates does so for their own reason, and using their own objectives and rules. Some want to solve the puzzles quickly, some want to be as efficient as possible, some just want to get the answer. I’ve seen solutions in Haskell, in R, in Javascript, in PHP, in Python… everything is possible.

My personal soft rules are:

• I use “vanilla” Python. Anything from the standard library is allowed (which means access to re for Regular Expressions, itertools, math, etc.), but I don’t use numpy, pandas or other fancier stuff.
• I don’t care too much about efficiency, but I try to be reasonably clean. My main goal is to be able to detect useful abstractions in the problem so that I can write functions and/or classes that make my solutions fairly modular. This is very useful in practice as – when I do it right – it means that I don’t spend too much time on the second part of the challenge, which usually brings a twist on the first part by adding new rules, new symbols, etc. When the first part was done right, the second can often be solved while keeping most of the functions identical.