Crate lib_aoc

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lib_aoc is a simple trait-based framework for the annual Advent of Code programming challenge.

Focus less on the boilerplate and more on the problem by automatically wiring up your solutions with input loading, pretty-printing and granular benchmarking.

Getting Started

Create a new binary crate and add lib_aoc as a dependency.

$ cargo new advent_of_code && cd advent_of_code
$ cargo add lib_aoc

Then, import the lib_aoc prelude and create a new struct to link your solutions.

use lib_aoc::prelude::*;
 
// Can be named whatever you'd like.
struct Solutions {}
 
fn main() { /* ... */ }

When solving a problem, you’ll implement the Solution trait on this struct, and lib_aoc will take care of connecting everything together.

Before you can do that, however, you’ll need to implement the Solver trait on the struct, which (among other, optional things) tells lib_aoc how you’d like puzzle inputs to be loaded.

The simple approach is to just read the input from disk, but more complex approaches (such as scraping the Advent of Code website directly) are certainly possible.

impl Solver for Solutions {
    fn load(day: u8, testing: bool) -> String {
       let path = match testing {
           false => Path::new("src/inputs").join(format!("{day:02}.txt")),
           true => Path::new("src/inputs").join(format!("{day:02}_test.txt"))
       };
 
       std::fs::read_to_string(path).expect("Puzzle input could not be read.")
   }
}

With Solver implemented, you can now begin solving problems!

Implementing a Solution

For demonstration purposes, we’ll assume a simple first problem:

The input is a list of integers, one per line.
Part one wants the sum of all the integers.
Part two wants us to square each integer, then sum them.

Start by implementing Solution<DAY_01> for your solutions struct; at minimum, you need to provide type definitions for Input and Output, as well as an implementation of parse.

impl Solution<DAY_01> for Solutions {
    type Input<'i> = Vec<u64>;
    type Output = u64;
 
    fn parse(puzzle: &str) -> Self::Input<'_> {
        puzzle
            .lines()
            .map(str::parse::<u64>())
            .map(Result::unwrap)
            .collect::<Vec<_>>() 
    }
}

At this point, the solution is technically ready to be run. You can use the solve_through macro to execute all solutions up to a certain day, like so:

fn main() {
    // Notes: 
    // - Due to macro limitations, you must use an integer literal for the day cap.
    // - Trying to solve through days you haven't implemented yet is a compile error.
    solve_through!(Solutions, 1);
}

Assuming your load implementation works, the program should output something like this:

--- DAY 1 ---
Part 1: unimplemented
Part 2: unimplemented

--- BENCH (DEBUG) ---
Parsing: 0 μs / 133 ns
Part 1: 0 μs / 53 ns
Part 2: 0 μs / 46 ns
Total: 0 μs / 436 ns

It looks like the actual solution logic is unimplemented! Fortunately, that’s easy to fix - we just implement the part_one and part_two methods.

impl Solution<DAY_01> for Solutions {
    type Input<'i> = Vec<u64>;
    type Output = u64;
 
    fn parse(puzzle: &str) -> Self::Input<'_> {
        puzzle
            .lines()
            .map(str::parse::<u64>())
            .map(Result::unwrap)
            .collect::<Vec<_>>() 
    }
 
    fn part_one(input: &Self::Input<'_>) -> Option<Self::Output> {
        input.iter()
            .sum::<u64>()
            .into()
    }

    fn part_two(input: &Self::Input<'_>) -> Option<Self::Output> {
        input.iter()
            .map(|x| x.pow(2) )
            .sum::<u64>()
            .into()
    }
}

As you can see, the signatures of the solver methods are identical apart from their names - they take a shared reference to a value of type Input and return an Option<Output>.

The default implementations simply return None, which is how lib_aoc knew to display unimplemented when the program was run earlier. By overriding them with implementations that return Some, the result will be displayed instead:

--- DAY 1 ---
Part 1: 66306
Part 2: 195292

--- BENCH (DEBUG) ---
Parsing: 533 μs / 533339 ns
Part 1: 0 μs / 67 ns
Part 2: 0 μs / 976 ns
Total: 534 μs / 534839 ns

And that’s it - you’ve implemented a solution!

Deriving Tests

Because Advent of Code provides a test case in the description of every problem, lib_aoc also comes with a macro for deriving tests from your Solution implementations.

Assuming your loader already correctly loads the test case instead of the full input when prompted, all you need to do is implement the Test trait on your solution to provide the expected results:

impl Test<DAY_01> for Solutions {
    fn expected() -> (Option<Self::Output>, Option<Self::Output>) {
        (Some("PART_ONE_EXPECTED"), Some("PART_TWO_EXPECTED"))
    }
}