Advent of Code 2025

This repository contains my personal solutions for Advent of Code 2025.

I use this project to:

• have some fun solving daily December puzzles,
• keep my algorithmic thinking and coding discipline sharp,
• experiment with clean modular solution structure.

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Tech stack

• Language: JavaScript (ES modules)
• Runtime: Node.js ≥ 20
• Linting: ESLint (eslint:recommended + eslint-config-prettier)
• Formatting: Prettier
• Editor settings: EditorConfig
• UI: small static HTML page acting as a runner for all days/parts

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Project structure

.
├── index.html       # browser runner entry point
├── app.js           # runner logic (dynamic imports)
├── style.css        # simple styling for the runner UI
├── days/
│   ├── _lib/        # shared helpers for parsing/math/etc.
│   ├── day01/
│   │   ├── part1.js # solver for day 01, part 1
│   │   └── part2.js # solver for day 01, part 2
│   ├── day02/
│   │   ├── part1.js
│   │   └── part2.js
│   └── ...
├── tests/           # small ad-hoc example runners per day/part
├── .editorconfig
├── .eslintrc.cjs
├── .gitignore
├── .prettierrc
├── package.json
└── README.md

Each day lives in its own folder:

• days/dayXX/part1.js – solution for Part 1
• days/dayXX/part2.js – solution for Part 2

Solvers are implemented as async functions that return an object with metadata and the answer:

export default async function solvePart1(input) {
  const lines = input.trim().split("\n");
  const answer = lines.length; // real logic goes here

  return {
    day: 1,
    part: 1,
    title: "Puzzle title",
    question: "Puzzle question text",
    answer,
  };
}

The same functions can be used:

• in the browser runner (via dynamic import),
• in Node scripts / CLI helpers (reading input.txt and printing the result),
• from ad-hoc example scripts in tests/dayXX.

The CLI runner unwraps the answer field if an object is returned. The simple browser runner currently renders whatever the solver returns, so you may want to return a primitive (string/number) or adjust the UI to pick result.answer.

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Browser runner

There is a small static page that lets you:

• choose a day and part,
• paste your puzzle input,
• get the answer directly in the browser.

Usage (locally)

You can open index.html directly in a browser, or serve the repo with any simple static server, for example:

npx serve .

Then open the printed URL and use the form:

1. Enter the day number (1–25).
2. Select the part (Part 1 / Part 2).
3. Paste your personal puzzle input from Advent of Code.
4. Click Run and see the result.

Usage (GitHub Pages)

If this repository is hosted on GitHub Pages, it will be available at something like:

https://<github-username>.github.io/<repo-name>/

The runner (index.html) will be served from the repository root.

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Running solutions with Node.js

You can run any day and part using the universal runner:

node run.mjs <day> [part] [inputPath]

Examples:

node run.mjs 1
node run.mjs 1 2
node run.mjs 3 1 ./inputs/example.txt

The runner automatically selects the solver and resolves the input file (part-specific or default).

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Progress

Checklist of solved days:

• Day 01 Part 1
• Day 01 Part 2
• Day 02 Part 1
• Day 02 Part 2
• Day 03 Part 1
• Day 03 Part 2
• Day 04 Part 1
• Day 04 Part 2
• Day 05 Part 1
• Day 05 Part 2
• Day 06 Part 1
• Day 06 Part 2
• Day 07 Part 1
• Day 07 Part 2
• Day 08 Part 1
• Day 08 Part 2
• Day 09 Part 1
• Day 09 Part 2
• Day 10 – Part 1 / Part 2
• Day 11 – Part 1 / Part 2
• Day 12 – Part 1 / Part 2

As days are solved, this section can be updated with links to the corresponding solution files and puzzle titles.

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Tooling

Install dev dependencies once:

npm install

Lint all files:

npm run lint

Attempt to fix lint issues automatically:

npm run lint:fix

Check formatting with Prettier:

npm run format

Reformat all files:

npm run format:write

Editors can be configured to:

• respect .editorconfig,
• run ESLint on save,
• format files with Prettier on save.

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Advent of Code inputs and content

Advent of Code provides personal puzzle inputs for each participant. To respect the rules and content ownership:

• personal input.txt files are not committed to this repository,
• puzzle inputs are used only locally,
• the repository does not mirror or redistribute the full puzzle descriptions.

If you want to solve these puzzles yourself, please visit:

• https://adventofcode.com/2025

Log in with your own account and use your own inputs.

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License

The code in this repository is available under the MIT License (see LICENSE).

Advent of Code puzzles, texts, and inputs are created and owned by Eric Wastl. Visit https://adventofcode.com/ for more details and to support the project.