#AdventOfCode 2018 #elixir #elixirlang

1_chronal_calibration.ex

defmodule ChronalCalibration do
  def calc_result(stream), do: Enum.sum(stream)

  def find_first_redundant(stream) do
    Stream.cycle(stream)
    |> Stream.scan({0, MapSet.new([0])}, &collect_step/2)
    |> Stream.filter(&redundant?/1)
    |> Stream.map(fn {elem, _} -> elem end)
    |> Enum.take(1)
    |> Enum.at(0)
  end

  def file_to_stream!(file) do
    File.stream!(file)
    |> Stream.map(&String.trim(&1, "\n"))
    |> Stream.map(&parse_frequency/1)
  end

  defp parse_frequency(""), do: 0
  defp parse_frequency(str) when is_binary(str), do: String.to_integer(str)
  defp parse_frequency(_), do: 0

  defp collect_step(elem, {last, steps}), do: {elem + last, MapSet.put(steps, last)}

  defp redundant?({last, steps}), do: MapSet.member?(steps, last)
  defp redundant?(_), do: false
end

test = fn ->
  defmodule ChronalCalibrationTest do
    use ExUnit.Case, async: true

    describe "part#1 frequency" do
      test "results in 3" do
        set = [+1, +1, +1]
        assert 3 == ChronalCalibration.calc_result(set)
      end

      test "results in 0" do
        set = [+1, +1, -2]
        assert 0 == ChronalCalibration.calc_result(set)
      end

      test "results in -6" do
        set = [-1, -2, -3]
        assert -6 == ChronalCalibration.calc_result(set)
      end
    end

    describe "part#2 first frequency" do
      test "reaches 0 twice" do
        set = [+1, -1]
        assert 0 == ChronalCalibration.find_first_redundant(set)
      end

      test "reaches 10 twice" do
        set = [+3, +3, +4, -2, -4]
        assert 10 == ChronalCalibration.find_first_redundant(set)
      end

      test "reaches 5 twice" do
        set = [-6, +3, +8, +5, -6]
        assert 5 == ChronalCalibration.find_first_redundant(set)
      end

      test "reaches 14 twice" do
        set = [+7, +7, -2, -7, -4]
        assert 14 == ChronalCalibration.find_first_redundant(set)
      end
    end
  end
end

case System.argv() do
  ["--test"] ->
    ExUnit.start()
    test.()

  _ ->
    set = ChronalCalibration.file_to_stream!("./1_input.txt")

    result = ChronalCalibration.calc_result(set)
    IO.puts("\n Frequency result is... #{result}")

    redundant = ChronalCalibration.find_first_redundant(set)
    IO.puts("\n Redundant frequency is... #{redundant} \n")
end

1_input.txt

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-12
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-76719

Readme.md

Getting Started

1. Make sure you have elixir installed and running. (Hint: elixir --version)
2. Download all gist files and run elixir 1_chronal_calibration.ex. That will compile the code and give you results.
3. Run elixir 1_chronal_calibration.ex --test to run tests.
4. Have more fun!