day_5.livemd

Day 5

Mix.install([:kino])

Input

input = Kino.Input.textarea("Please provide the data here")

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

number_of_stacks =
  stack
  |> String.split("\n", trim: true)
  |> Enum.at(-1)
  |> String.split(" ", trim: true)
  |> Enum.at(-1)
  |> String.to_integer()

stack =
  stack
  |> String.replace("    ", " ")
  |> String.split("\n", trim: true)
  |> Enum.drop(-1)
  |> Enum.map(&String.split(&1, " "))
  |> Enum.zip()
  |> Enum.map(fn tuple ->
    tuple
    |> Tuple.to_list()
    |> Enum.reduce([], fn
      "[" <> <<letter>> <> "]", acc -> acc ++ [letter]
      _, acc -> acc
    end)
  end)

stack =
  1..number_of_stacks
  |> Enum.zip(stack)
  |> Enum.into(%{})

moves =
  ~r/move (\d+) from (\d+) to (\d+)/
  |> Regex.replace(moves, "\\1 \\2 \\3")
  |> String.split("\n", trim: true)
  |> Enum.map(fn string ->
    string
    |> String.split(" ")
    |> Enum.map(&String.to_integer/1)
  end)

Part 1

defmodule Day5.Part1 do
  def move(stack, [1, from, to]) do
    %{^from => [item | rest], ^to => to_stack} = stack

    stack
    |> Map.put(from, rest)
    |> Map.put(to, [item | to_stack])
  end

  def move(stack, [quantity, from, to]) do
    stack
    |> move([1, from, to])
    |> move([quantity - 1, from, to])
  end
end

moves
|> Enum.reduce(stack, &Day5.move(&2, &1))
|> Enum.reduce([], fn {_key, [hd | _rest]}, acc -> acc ++ [hd] end)

Part 2

defmodule Day5.Part2 do
  def move(stack, [1, from, to]) do
    %{^from => [item | rest], ^to => to_stack} = stack

    stack
    |> Map.put(from, rest)
    |> Map.put(to, [item | to_stack])
  end

  def move(stack, [quantity, from, to]) do
    %{^from => from_stack, ^to => to_stack} = stack
    {item, rest} = List.pop_at(from_stack, quantity - 1)

    stack =
      stack
      |> Map.put(from, rest)
      |> Map.put(to, [item | to_stack])

    move(stack, [quantity - 1, from, to])
  end
end

moves
|> Enum.reduce(stack, &Day5.Part2.move(&2, &1))
|> Enum.reduce([], fn {_key, [hd | _rest]}, acc -> acc ++ [hd] end)