AdventOfCode/2020/elixir/day21/day21part2.exs

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Elixir
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2020-12-26 06:32:52 +00:00
defmodule DayDay21Part2 do
def run do
File.read!("input")
|> String.split("\n", trim: true)
|> Enum.map(&String.split(&1, [" (contains ", ", ", ")"], trim: true))
|> Enum.map(fn [ingredients | allergens] -> {String.split(ingredients), allergens} end)
|> Enum.reduce(%{}, fn {ingredients, allergens}, acc ->
ingredients = MapSet.new(ingredients)
Enum.reduce(allergens, acc, fn allergen, acc ->
Map.update(acc, allergen, ingredients, &MapSet.intersection(&1, ingredients))
end)
end)
|> Map.new(fn {allergen, ingredients} -> {allergen, MapSet.to_list(ingredients)} end)
|> resolve_ingredients([])
|> Enum.sort_by(fn {allergen, _ingredient} -> allergen end)
|> Enum.map(fn {_allergen, ingredient} -> ingredient end)
|> Enum.join(",")
|> IO.puts()
end
def resolve_ingredients(suspected, resolved) when map_size(suspected) == 0, do: resolved
def resolve_ingredients(suspected, resolved) do
{allergen, [ingredient]} =
Enum.find(suspected, fn {_allergen, ingredients} -> length(ingredients) == 1 end)
IO.puts("#{ingredient} contains #{allergen}")
suspected =
suspected
|> Map.delete(allergen)
|> Map.new(fn {allergen, ingredients} -> {allergen, ingredients -- [ingredient]} end)
resolved = [{allergen, ingredient} | resolved]
resolve_ingredients(suspected, resolved)
end
end
DayDay21Part2.run()