day-5

Mix.install([
  {:kino, "~> 0.7.0"}
])

Input

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

Read input

[data, moves] =
  input
  |> Kino.Input.read()
  |> String.split("\n\n")

[header | data] =
  data
  |> String.split(["\n"])
  |> Enum.reverse()

stacks =
  header
  |> String.split(" ", trim: true)
  |> Enum.map(&String.to_integer/1)
  |> Enum.map(fn index ->
    data =
      data
      |> Enum.map(&String.at(&1, (index - 1) * 3 + index))
      |> Enum.reject(&(&1 == " "))

    {index, data}
  end)
  |> Map.new()

moves =
  moves
  |> String.split("\n")
  |> Enum.map(&String.split(&1, ["move ", " from ", " to "], trim: true))
  |> Enum.map(fn moves -> Enum.map(moves, &String.to_integer/1) end)
  |> Enum.map(&List.to_tuple/1)

Part 1

new_stacks =
  Enum.reduce(moves, stacks, fn {amount, from, to}, acc ->
    moved = acc[from] |> Enum.take(-amount) |> Enum.reverse()
    from_stack = Enum.drop(acc[from], -amount)
    to_stack = Enum.concat(acc[to], moved)

    acc
    |> Map.put(from, from_stack)
    |> Map.put(to, to_stack)
  end)

new_stacks
|> Enum.map(fn {_k, v} -> Enum.at(v, -1) end)
|> Enum.join("")

Part 2

new_stacks =
  Enum.reduce(moves, stacks, fn {amount, from, to}, acc ->
    moved = Enum.take(acc[from], -amount)
    from_stack = Enum.drop(acc[from], -amount)
    to_stack = Enum.concat(acc[to], moved)

    acc
    |> Map.put(from, from_stack)
    |> Map.put(to, to_stack)
  end)

new_stacks
|> Enum.map(fn {_k, v} -> Enum.at(v, -1) end)
|> Enum.join("")