Day 7

Setup

Mix.install([:kino])

input = Kino.Input.textarea("Input", default: "16,1,2,0,4,2,7,1,2,14")

input =
  input
  |> Kino.Input.read()
  |> String.trim()
  |> String.split(",", trim: true)
  |> Stream.map(&String.to_integer/1)

Part 1

min = Enum.min(input)
max = Enum.max(input)

min..max
|> Stream.map(fn target ->
  total_fuel = Enum.reduce(input, 0, fn el, acc -> abs(el - target) + acc end)
  {target, total_fuel}
end)
|> Enum.reduce(fn {pos, fuel}, {best_position, best_fuel} ->
  if fuel < best_fuel, do: {pos, fuel}, else: {best_position, best_fuel}
end)

Part 2

min = Enum.min(input)
max = Enum.max(input)

min..max
|> Stream.map(fn target ->
  total_fuel =
    Enum.reduce(input, 0, fn el, acc ->
      moves = abs(el - target)
      fuel = div(moves * (moves + 1), 2)
      fuel + acc
    end)

  {target, total_fuel}
end)
|> Enum.reduce(fn {pos, fuel}, {best_position, best_fuel} ->
  if fuel < best_fuel, do: {pos, fuel}, else: {best_position, best_fuel}
end)