advent-of-code

Just having some fun solving Advent of Code with Kotlin

2025 puzzles

2025 puzzles are here

How to has?

Solve puzzles as unit tests, create each day in a file like advent/src/test/kotlin/org/elwaxoro/advent/y2022/Dec01.kt

Extend PuzzleDayTester, override part1 and part2 functions as you write them:

class Dec01 : PuzzleDayTester(1, 2020) {
    override fun part1(): Any = "Yay"
    override fun part2(): Any = "Boo"
}

By default, these tests fail till they're implemented. Any return counts as passing. Since the test doesn't know the right answer, check the output for what to copy into the advent of code test boxes

Input files

Input files should go in test/resources based on year and date like advent/src/test/resources/2022/Dec01.txt

Note: input files are totally optional! Only use them if it makes sense for the puzzle you're solving

PuzzleDayTester has a load function to help find them and parse them in a simple way (one string per newline by default)

load(testNum: Int? = null, delimiter: String = "\n"): List<String>

Optional: if testNum is set on the load function, a file with the format Dec01-test-1.txt is looked for instead of Dec01.txt This lets you separate the real input file from the samples (which can vary part 1 vs part 2)

Extensions / Helpers

main/kotlin has a collection of extensions and helper classes to solve certain kinds of puzzles. Ignore these if you want. Or use them. I won't tell you what to do.

Disclaimers

Running the code for previous days / years isn't guaranteed to work or give correct output. Same goes for some of the helper functions. Most things should work, but ymmv! I tend to solve these quickly, then come back later to refactor. Sometimes the refactor breaks it and then I run out of time to fight with it, so it stays broken. Good luck!

Z3 Setup / Usage

When a puzzle requires theorem proving (or falls easily into that category), Z3 may be installed and used directly within this repo. Install steps:

1. Download Z3 from https://github.com/Z3Prover/z3
2. Unzip into advent-of-code/z3
3. Uncomment Z3 references from advent/build.gradle.kts
4. If on OSX arm64, you may need to run install_name_tool -change libz3.dylib @loader_path/libz3.dylib libz3java.dylib to correctly link the libraries in advent-of-code/z3/bin