Day 5: Supply Stacks

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

Input

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

Split input and parsing crates

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

crates =
  crates
  |> String.split("\n", trim: true)
  |> Enum.drop(-1)
  |> Enum.map(fn x ->
    String.split(x, "", trim: true)
    |> Enum.chunk_every(3, 4, :discard)
    |> Enum.map(&Enum.join/1)
  end)
  |> Enum.zip()
  |> Enum.map(&(Tuple.to_list(&1) |> Enum.filter(fn x -> String.trim(x) !== "" end)))

Part 1

instruction
|> String.split("\n", trim: true)
|> Enum.map(fn x ->
  Regex.split(~r/[^0-9]+/, x, trim: true)
  |> Enum.map(&String.to_integer/1)
end)
|> Enum.reduce(crates, fn [amount, from, to], acc ->
  stack =
    Enum.at(acc, from - 1)
    |> Enum.take(amount)
    |> Enum.reverse()

  acc = List.replace_at(acc, from - 1, Enum.at(acc, from - 1) -- stack)
  crates = Enum.at(acc, to - 1)
  new_stack = stack ++ crates
  List.replace_at(acc, to - 1, new_stack)
end)
|> Enum.zip()
|> Enum.map(&Tuple.to_list(&1))
|> List.first()
|> Enum.join()
|> String.replace(~r/\[|\]/, "")

Part 2

instruction
|> String.split("\n", trim: true)
|> Enum.map(fn x ->
  Regex.split(~r/[^0-9]+/, x, trim: true)
  |> Enum.map(&String.to_integer/1)
end)
|> Enum.reduce(crates, fn [amount, from, to], acc ->
  stack =
    Enum.at(acc, from - 1)
    |> Enum.take(amount)

  acc = List.replace_at(acc, from - 1, Enum.at(acc, from - 1) -- stack)
  crates = Enum.at(acc, to - 1)
  new_stack = stack ++ crates
  List.replace_at(acc, to - 1, new_stack)
end)
|> Enum.zip()
|> Enum.map(&Tuple.to_list(&1))
|> List.first()
|> Enum.join()
|> String.replace(~r/\[|\]/, "")