#AdventOfCode 2018 #elixir #elixirlang

2_inventory_management.ex

defmodule InventoryManagement.Checksum do
  def checksum(stream) do
    stream
    |> Stream.map(&String.trim/1)
    |> Stream.map(&count_occurances/1)
    |> Enum.reduce([two: 0, three: 0], &collect_each/2)
    |> Enum.reduce(1, fn {_, val}, acc -> val * acc end)
  end

  defp collect_each([two: item_two, three: item_three], two: two, three: three) do
    [two: two + item_two, three: three + item_three]
  end

  defp count_occurances(id) do
    id
    |> String.graphemes()
    |> Enum.reduce(%{}, &count_letters/2)
    |> Enum.reduce([two: 0, three: 0], &calc_valids/2)
  end

  defp count_letters(letter, acc), do: Map.update(acc, letter, 1, &(&1 + 1))

  defp calc_valids({_, count}, two: two, three: three) do
    case count do
      3 ->
        [two: two, three: 1]

      2 ->
        [two: 1, three: three]

      _ ->
        [two: two, three: three]
    end
  end
end

defmodule InventoryManagement.PrototypeFabric do
  def find(stream) do
    stream
    |> Stream.map(&String.trim/1)
    |> Enum.reduce_while(MapSet.new(), &collect_combinations/2)
  end

  defp collect_combinations(id, combinations) do
    id_combs = make_id_combs(id)

    case Enum.find(id_combs, &MapSet.member?(combinations, &1)) do
      comb when is_binary(comb) ->
        {:halt, comb}

      nil ->
        combinations = Enum.reduce(id_combs, combinations, &MapSet.put(&2, &1))
        {:cont, combinations}
    end
  end

  defp make_id_combs(id) do
    for i <- 0..(String.length(id) - 1) do
      for j <- 0..(String.length(id) - 1), j != i, into: "", do: String.at(id, j)
    end
  end
end

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

    describe "part#1 checksum" do
      test "calculated correctly with example input" do
        example =
          """
            abcdef
            bababc
            abbcde
            abcccd
            aabcdd
            abcdee
            ababab

          """
          |> String.splitter("\n", trim: true)

        assert 12 == InventoryManagement.Checksum.checksum(example)
      end
    end

    describe "part#2 find prototype fabric" do
      test "for example input" do
        example =
          """
            abcde
            fghij
            klmno
            pqrst
            fguij
            axcye
            wvxyz

          """
          |> String.splitter("\n", trim: true)

        assert "fgij" == InventoryManagement.PrototypeFabric.find(example)
      end
    end
  end
end

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

  _ ->
    checksum =
      File.stream!("./2_inventory_management_input.txt")
      |> InventoryManagement.Checksum.checksum()

    IO.puts("Checksum result of the input file is... #{checksum}")

    common_letters =
      File.stream!("./2_inventory_management_input.txt")
      |> InventoryManagement.PrototypeFabric.find()

    IO.puts("Common letters for prototype fabric is... #{common_letters}")
end

2_inventory_management_input.txt

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README.md

Getting Started

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