Day 7

Setup

Mix.install([
  {:kino, "~> 0.4.1"}
])

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

parsed_input =
  input
  |> Kino.Input.read()
  |> String.split(",")
  |> Enum.map(&String.to_integer/1)

parsed_input
|> Enum.min_max()

Part 1

freq =
  parsed_input
  |> Enum.frequencies()

possible_solutions =
  freq
  |> Map.keys()
  |> Enum.min_max()
  |> then(fn {min, max} -> Range.new(min, max) end)

Enum.reduce(possible_solutions, :infinity, fn sol, best ->
  fuel_spent =
    Enum.map(freq, fn {position, crabs} -> abs(position - sol) * crabs end)
    |> Enum.sum()

  if fuel_spent < best do
    fuel_spent
  else
    best
  end
end)

Part 2

Enum.reduce(possible_solutions, :infinity, fn sol, best ->
  fuel_spent =
    Enum.map(freq, fn {position, crabs} -> (1..abs(position - sol) |> Enum.sum()) * crabs end)
    |> Enum.sum()

  if fuel_spent < best do
    fuel_spent
  else
    best
  end
end)