Advent of Code 2025 — Rust Starter Template

This is a lightweight template geared towards beginners. Each day has:

• A library module with two functions: part1(&str) -> anyhow::Result<T> and part2(&str) -> anyhow::Result<T>
• Unit tests using the included example input(s)
• A small binary you can run to print answers for your real input

Requirements

• Rust (stable). Install with rustup if you don’t have it.

Layout . ├── Cargo.toml ├── src │ ├── lib.rs # shared helpers + days module │ ├── days │ │ ├── mod.rs │ │ └── day01.rs # example/template day implementation + tests │ └── bin │ └── day01.rs # binary runner for day 01 └── inputs └── day01 ├── example.txt # used by unit tests └── input.txt # your real puzzle input

Running tests

• Run all tests: cargo test
• Run only Day 01 tests: cargo test day01

Running a day’s binary

• Put your puzzle input in inputs/day01/input.txt
• Run: cargo run --bin day01

Adding a new day

1. Create a new module file src/days/dayXX.rs (copy day01.rs as a starting point)

   • Implement pub fn part1(input: &str) -> anyhow::Result<...>
   • Implement pub fn part2(input: &str) -> anyhow::Result<...>
   • Keep or add unit tests that read from inputs/dayXX/example.txt

2. Register it in src/days/mod.rs with pub mod dayXX;

3. Add a binary at src/bin/dayXX.rs: use anyhow::Result; use aoc2025::read_input; use aoc2025::days::dayXX;

   fn main() -> Result<()> { let input = read_input(XX)?; // replace XX with the day number println!("Part 1: {}", dayXX::part1(&input)?); println!("Part 2: {}", dayXX::part2(&input)?); Ok(()) }

4. Add inputs:

   • inputs/dayXX/example.txt for tests
   • inputs/dayXX/input.txt for the real input

Tips for learning

• Keep parsing separate from logic to simplify testing.
• Start with &str input functions, return anyhow::Result so you can use ? for error handling.
• Add small unit tests for sub-functions if a day becomes more complex.

Happy hacking!