Day 5

Mix.install([{:kino, "~> 0.5.0"}])

Input

input = """
    [D]    
[N] [C]    
[Z] [M] [P]
 1   2   3 

move 1 from 2 to 1
move 3 from 1 to 3
move 2 from 2 to 1
move 1 from 1 to 2
"""

input = Kino.Input.textarea("Paste input here:")

input = Kino.Input.read(input)

input = String.split(input, "\n", trim: true)
{crates, [_ | instructions]} = Enum.split_while(input, fn s -> String.at(s, 1) != "1" end)

crates =
  crates
  |> Enum.map(fn s ->
    s
    |> String.codepoints()
    |> Enum.chunk_every(4)
    |> Enum.map(&Enum.at(&1, 1))
  end)
  |> Enum.zip()
  |> Enum.map(fn l ->
    l
    |> Tuple.to_list()
    |> Enum.reject(&(&1 == " "))
  end)

Part 1

defmodule Crates do
  def execute(crates, []), do: crates

  def execute(crates, [instruction | instructions]) do
    [count, src_stack, dst_stack] =
      Regex.run(~r/move (\d+) from (\d+) to (\d+)/, instruction, capture: :all_but_first)
      |> Enum.map(&String.to_integer/1)

    {src_stack, dst_stack} = {src_stack - 1, dst_stack - 1}

    {to_move, new_src} = Enum.at(crates, src_stack) |> Enum.split(count)

    IO.inspect(crates)

    crates =
      crates
      |> List.replace_at(src_stack, new_src)
      |> List.update_at(dst_stack, fn l -> Enum.reverse(to_move) ++ l end)

    execute(crates, instructions)
  end
end

Crates.execute(crates, instructions)

Crates.execute(crates, instructions)
|> Enum.map(&List.first/1)
|> Enum.join()

Part 2

defmodule CrateMover9001 do
  def execute(crates, []), do: crates

  def execute(crates, [instruction | instructions]) do
    [count, src_stack, dst_stack] =
      Regex.run(~r/move (\d+) from (\d+) to (\d+)/, instruction, capture: :all_but_first)
      |> Enum.map(&String.to_integer/1)

    {src_stack, dst_stack} = {src_stack - 1, dst_stack - 1}

    {to_move, new_src} = Enum.at(crates, src_stack) |> Enum.split(count)

    IO.inspect(crates)

    crates =
      crates
      |> List.replace_at(src_stack, new_src)
      |> List.update_at(dst_stack, fn l -> to_move ++ l end)

    execute(crates, instructions)
  end
end

CrateMover9001.execute(crates, instructions)

CrateMover9001.execute(crates, instructions)
|> Enum.map(&List.first/1)
|> Enum.join()