Trevor Stone's Advent of Code Repository

This is a repository containing solutions for Advent of Code. Each AoC year has its own directory and the solution for each day is in its own subdirectory. Each day’s solution is generally a standalone program which takes input either on standard input (2020) or one or more input files on the command line (2021 and forward). 2022 introduced a separate solution runner library rather than including a few dozen lines of orchestration code in the template, but they still run as standalone scripts with more spartan output. The scripts take an optional -v or --verbose flag as the first argument to print whether the program matched the expected output, along with timing information. There is also a testday script which can run one or more days, compare output with expected, and report results using the Test Anything Protocol format.

I generally use Advent of Code as an opportunity to get experience with a language that I don’t yet know well. You’re welcome to take inspiration from the way I solved a problem, but please don’t assume that I’ve solved it in the most idiomatic, efficient, or readable way.

Year	Language	Thoughts
2020	Kotlin	Blog post
2021	Raku plus Go when Raku was too slow	Blog post
2022	Elixir	Blog post
2023	Julia
2024	PostScript

This code is made available under an MIT-style license. I do not accept pull requests to this repo, but you’re welcome to point out anything you think could be done better.

Directory Structure

Each year’s solutions are in a directory named after the year. Within that dir is one directory for each day’s solution, named day1 through day25. Each day directory has the solution code in one or more languages, a file named input.example.txt with an example taken from the problem description and input.example.expected with two lines (prefixed part1: and part2: ) with the expected output when the solution code is run input.example.txt. If the problem description has multiple examples, they’ll be in input.example2.txt and input.example2.expected, etc.

The input.actual.txt and input.actual.expected files are symlinks into a non-public directory with input specific to my AoC account. If you’d like to test my code against your personal input, provide the path to your input as a command line argument: day1/day1.exs -v path/to/my/input.txt. If you’d like to run a whole suite of solutions against your input, make sure they’re in a directory with numbered subdirectories, e.g. 1/input.actual.txt and replace my input directory with a symlink to yours, e.g. rm 2023/input; ln -s path/to/my/2023 2023/input which will cause runday and testday scripts to use yours. Alternatively, substitute the input submodule at the base of the repository, as in the next section.

There is also a lang directory for runner and generator infrastructure for programming languages which aren’t “the main language” for any year, but which I sometimes use for fun or because I got stuck on a problem with the main new language for a year.

Hiding Private Advent of Code Input with Git Submodules

Eric Wastl asks that you don’t include your personal input in public source code repositories. If you’d like to use git submodules to keep your input files under source control and available wherever you check out the repository with your code, follow these steps:

1. Create a new GitHub repository and select the Private radio button. Give it a name like adventofcode-input.

2. Git submodules don’t work with an empty repository, so make sure to create at least one file in this new repository, such as .gitignore or README.md.

3. In your main Advent of Code repository, add the new repository as a submodule: git submodule add https://github.com/YourUserName/adventofcode-input input. This will check out the new repo into a directory named input.

4. If you run git status it will show two new staged entries: .gitmodules and input. If you run git diff --staged you’ll see the content of the new .gitmodules file (this keeps track of your submodules and their remote URL) and the latest git commit in that repo:

   diff --git a/.gitmodules b/.gitmodules
   new file mode 100644
   index 0000000..7904cad
   --- /dev/null
   +++ b/.gitmodules
   @@ -0,0 +1,3 @@
   +[submodule "input"]
   +       path = input
   +       url = https://github.com/flwyd/adventofcode-input
   diff --git a/input b/input
   new file mode 160000
   index 0000000..7fde85f
   --- /dev/null
   +++ b/input
   @@ -0,0 +1 @@
   +Subproject commit 7fde85fc0dc5d6334645ebd10978e8755aab4de2
   

5. Run git commit to add this new submodule to your main repository’s history.

6. Run git push origin main to upload your main repository to GitHub. Since the input submodule is private, other people won’t be able to see the files inside that directory when they browse github.com or check out your public repository.

7. When you check out your main repository on a different computer, you need to initialize the submodule. The easy way to do this is when cloning: git clone --recurse-submodules https://github.com/YourUserName/adventofcode If it’s already checked out, run git submodule init && git submodule update Git may prompt you for your GitHub credentials when checking out the submodule if your credentials aren’t cached

8. Although the submodule is really a separate git repository, locally it looks like a single file tree. As you work on AoC problems, put your personal input files in the submodule, e.g. in input/2023/1/input.actual.txt. Your code can read the input files using a relative path, or you can create a symlink from your solution directory: cd solutions2023; ln -s ../input/2023/1/input.actual.txt day1/

9. When your solution’s done it now takes two steps to upload to GitHub. First, commit the input file in your submodule:

   cd input
   git add 2023/1
   git commit -m "2023 day 1 input file"
   git push origin main

   Then commit the code and other files in your main repository, as well as the pointer to the new head commit of your input repository:

   cd ..
   git add input
   git add 2023/day1/*
   git commit -m "Solution to 2023 day 1"
   git push origin main

10. If you’d like to check out someone’s Advent of Code solutions repository but use your own input files, you can swap out the submodule URL: git config submodule.input.url https://github.com/SomwhereElse/aoc-input and then run git submodule init && git submodule update.