Day 8

Setup

Mix.install([:kino])

input = Kino.Input.textarea("Input")

Part 1

unique_digit_line_count = [2, 4, 3, 7]

input
|> Kino.Input.read()
|> String.split("\n")
|> Stream.map(&String.split(&1, " | "))
|> Stream.map(fn [_, output] -> output end)
|> Stream.flat_map(&String.split(&1, " "))
|> Enum.count(fn digit -> Enum.member?(unique_digit_line_count, String.length(digit)) end)

Part 2

segments = ["a", "b", "c", "d", "e", "f", "g"]
initial_mappings = Enum.map(segments, fn segment -> {segment, segments} end) |> Enum.into(%{})

{input, output} =
  "acedgfb cdfbe gcdfa fbcad dab cefabd cdfgeb eafb cagedb ab | cdfeb fcadb cdfeb cdbaf"
  |> String.split(" | ")
  |> then(fn [i, o] ->
    {
      i |> String.split() |> Enum.group_by(&byte_size/1, &String.to_charlist/1),
      o |> String.split(" ") |> Enum.map(&String.to_charlist/1)
    }
  end)

%{
  2 => [one],
  3 => [seven],
  4 => [four],
  5 => two_five_three,
  6 => zero_nine_six,
  7 => [eight]
} = input

supersets = fn numbers, pivot ->
  Enum.filter(numbers, &match?([], pivot -- &1))
end

[nine] = supersets.(zero_nine_six, four)

Enum.sort(nine)