AdventOfCode in Elixir

Mix tasks

`$ mix newday <year> <day>`

Creates the solution template for a specific day. This will create:

lib/adventofcode/puzzles/year_<year>/day_<day>.ex
priv/inputs/year_<year>/day_<day>/input.txt

It will fill the solution (.ex) file with a simple template.

`$ mix runday <year> <day> <part> [input]`

Run the solution for a specific year, day and part (A or B) and a specific input file.
If nothing is specified, input.txt will be used but for testing with a subset or example, it can be useful to use a different file instead. E.g. mix runday 2015 01 example_01.txt

Workflow

Run mix newday 2015 01
Copy the puzzle input to input.txt
Solve the puzzle and run it with mix runday 2015 01

Directory structure

This repository uses a standardized directory structure for all puzzles, so solutions are easy to create and easy to understand. The following tree shows the most important directories:

/
├─ lib/
│  ├─ adventofcode
│  │  ├─ common         <- Common helper modules
│  │  ├─ puzzles
│  │     ├─ year_xxxx   <- Puzzle files for a specific year
│  ├─ mix
│     ├─ tasks
├─ priv/
   ├─ inputs
      ├─ year_xxxx      <- Puzzle inputs for a specific year
         ├─ day_xx      <- Puzzle inputs for a specific day

For example the puzzle for the 1. December 2015 is solved in:

Solution: lib/adventofcode/puzzles/year_2015/day_01.ex
Inputs: priv/inputs/year_2015/day_01/*.txt

Solution structure

Each puzzles is solved using a solution structure that is generated as a template by mix newday.

For easy input parsing, AdvenOfCode.Common.Input is always aliased. Additional common modules can be aliased as required by the puzzle.

defmodule AdventOfCode.Puzzles.Year2015.Day01 do
  require Logger

  alias AdventOfCode.Common.Input

  defmodule PartA do
    def solve(input) do
      IO.inspect(input)
    end
  end

  defmodule PartB do
    def solve(input) do
      IO.inspect(input)
    end
  end
end

Testing

By default, when running mix test only unit tests for common modules such as AdventOfCode.Common.Input will be run. However, since all inputs and solutions are stored in the repository, tests for the individual puzzles are also created.

The test/puzzles/year_xxxx_test.exs files will provide tests for a specific year's puzzles. They utilize a macro defined in the test helper to generate one test case per day and part from a list of day/part and solution pairs.

To run all puzzles and test their output, run RUN_PUZZLE_TESTS=true mix test. To run specific tests, use RUN_PUZZLE_TESTS=true mix test --only YYYY-DD (e.g. RUN_PUZZLE_TESTS=true mix test --only 2015-01).

Since AdventOfCode nicely asks us not to include puzzle inputs, running these tests is only possible for myself. The commited input files are always encrypted using git-secret.

Additional tidbits

Sharing code between parts

It is often required to share input parsing or some processing between part A and part B of a day's puzzle. To facilitate this, AdventOfCode.Common.Shared can be used, which contains a macro that will import all functions from the shared module in the same day.

Please note that the .Shared module must be defined above the PartA and PartB modules.

defmodule AdventOfCode.Puzzles.Year2015.Day01 do
  require Logger

  alias AdventOfCode.Common.Input

  defmodule Shared do
    def ident(x), do: x
  end

  defmodule PartA do
    use AdventOfCode.Common.Shared

    # ident/1 can now be used here
  end

  defmodule PartB do
    use AdventOfCode.Common.Shared

    # ident/1 can now be used here
  end
end

Potentially breaking decisions

Some puzzle solutions contain comment lines that start with a [!]. These are annotations for cases where I either suspect I misunderstood how the puzzle author intended the puzzle to be solved or intentionally sacrificed generality of the solution for simply getting the job done.

Simply put, functions that have [!] comments work for my puzzle input but they might not work for yours.

cybrox / adventofcode