Day 5

input = """
            [M] [S] [S]            
        [M] [N] [L] [T] [Q]        
[G]     [P] [C] [F] [G] [T]        
[B]     [J] [D] [P] [V] [F] [F]    
[D]     [D] [G] [C] [Z] [H] [B] [G]
[C] [G] [Q] [L] [N] [D] [M] [D] [Q]
[P] [V] [S] [S] [B] [B] [Z] [M] [C]
[R] [H] [N] [P] [J] [Q] [B] [C] [F]
 1   2   3   4   5   6   7   8   9 

move 1 from 7 to 4
move 3 from 4 to 7
move 4 from 3 to 4
move 5 from 6 to 9
move 1 from 8 to 1
move 2 from 3 to 2
move 3 from 4 to 6
move 1 from 3 to 6
move 9 from 7 to 1
move 1 from 2 to 4
move 3 from 4 to 9
move 4 from 9 to 8
move 6 from 8 to 2
move 1 from 8 to 6
move 1 from 4 to 1
move 11 from 1 to 7
move 1 from 4 to 7
move 7 from 2 to 5
move 5 from 6 to 3
move 2 from 4 to 3
move 2 from 5 to 9
move 1 from 8 to 6
move 3 from 1 to 5
move 2 from 6 to 9
move 1 from 4 to 8
move 2 from 2 to 1
move 7 from 5 to 9
move 6 from 3 to 6
move 1 from 2 to 5
move 1 from 3 to 8
move 12 from 7 to 3
move 1 from 1 to 8
move 2 from 1 to 9
move 20 from 9 to 5
move 1 from 1 to 7
move 5 from 5 to 3
move 1 from 8 to 7
move 2 from 8 to 3
move 2 from 6 to 5
move 1 from 6 to 4
move 18 from 3 to 2
move 1 from 4 to 2
move 1 from 7 to 9
move 1 from 1 to 9
move 1 from 6 to 1
move 8 from 5 to 2
move 1 from 1 to 6
move 19 from 5 to 2
move 5 from 2 to 6
move 2 from 9 to 7
move 20 from 2 to 1
move 1 from 9 to 4
move 8 from 6 to 2
move 5 from 1 to 3
move 27 from 2 to 1
move 34 from 1 to 7
move 1 from 2 to 6
move 2 from 3 to 1
move 1 from 4 to 9
move 1 from 2 to 6
move 2 from 1 to 7
move 1 from 6 to 7
move 1 from 9 to 3
move 2 from 6 to 3
move 1 from 6 to 4
move 5 from 3 to 4
move 5 from 4 to 2
move 4 from 1 to 4
move 4 from 1 to 4
move 2 from 3 to 6
move 1 from 6 to 9
move 25 from 7 to 5
move 1 from 6 to 4
move 17 from 5 to 2
move 14 from 7 to 6
move 1 from 7 to 3
move 1 from 9 to 3
move 10 from 2 to 3
move 2 from 2 to 9
move 12 from 3 to 5
move 18 from 5 to 8
move 1 from 4 to 2
move 5 from 2 to 1
move 1 from 5 to 3
move 3 from 2 to 1
move 1 from 2 to 7
move 2 from 2 to 6
move 9 from 6 to 7
move 16 from 8 to 2
move 6 from 7 to 3
move 2 from 8 to 9
move 1 from 1 to 8
move 16 from 2 to 6
move 1 from 8 to 3
move 2 from 1 to 2
move 1 from 9 to 3
move 7 from 4 to 1
move 7 from 3 to 7
move 9 from 7 to 8
move 1 from 5 to 6
move 2 from 9 to 7
move 1 from 9 to 5
move 11 from 6 to 8
move 1 from 3 to 1
move 1 from 4 to 2
move 2 from 8 to 5
move 3 from 5 to 8
move 2 from 1 to 9
move 5 from 1 to 4
move 3 from 4 to 1
move 1 from 3 to 2
move 3 from 2 to 1
move 1 from 9 to 1
move 1 from 2 to 5
move 2 from 4 to 7
move 20 from 8 to 5
move 1 from 9 to 7
move 11 from 6 to 1
move 17 from 1 to 5
move 1 from 8 to 2
move 7 from 5 to 8
move 1 from 4 to 5
move 2 from 1 to 2
move 2 from 8 to 4
move 4 from 7 to 6
move 2 from 6 to 8
move 2 from 1 to 2
move 1 from 1 to 4
move 4 from 8 to 9
move 2 from 1 to 9
move 3 from 8 to 1
move 25 from 5 to 2
move 23 from 2 to 1
move 1 from 7 to 1
move 6 from 9 to 8
move 6 from 8 to 3
move 3 from 6 to 2
move 10 from 1 to 2
move 1 from 6 to 3
move 2 from 3 to 6
move 2 from 3 to 2
move 2 from 6 to 8
move 1 from 4 to 6
move 14 from 1 to 9
move 2 from 3 to 4
move 14 from 2 to 4
move 1 from 6 to 9
move 17 from 4 to 3
move 1 from 8 to 6
move 2 from 7 to 2
move 1 from 4 to 2
move 1 from 5 to 9
move 9 from 2 to 4
move 17 from 3 to 7
move 3 from 4 to 2
move 1 from 8 to 3
move 4 from 5 to 7
move 1 from 3 to 6
move 1 from 4 to 5
move 14 from 7 to 9
move 2 from 1 to 9
move 3 from 2 to 1
move 1 from 2 to 5
move 1 from 3 to 7
move 4 from 1 to 2
move 2 from 6 to 7
move 3 from 9 to 8
move 4 from 2 to 4
move 17 from 9 to 7
move 1 from 2 to 8
move 8 from 9 to 6
move 1 from 8 to 2
move 19 from 7 to 9
move 9 from 4 to 2
move 5 from 7 to 3
move 3 from 5 to 9
move 6 from 2 to 5
move 1 from 9 to 4
move 3 from 2 to 9
move 25 from 9 to 5
move 1 from 3 to 6
move 2 from 5 to 8
move 6 from 6 to 7
move 1 from 3 to 4
move 2 from 3 to 4
move 1 from 8 to 2
move 2 from 2 to 9
move 2 from 8 to 3
move 5 from 7 to 6
move 3 from 7 to 9
move 7 from 5 to 8
move 2 from 3 to 5
move 1 from 3 to 5
move 1 from 6 to 2
move 6 from 9 to 5
move 1 from 9 to 2
move 1 from 6 to 9
move 2 from 5 to 6
move 2 from 9 to 8
move 11 from 8 to 1
move 2 from 5 to 9
move 3 from 6 to 5
move 1 from 4 to 7
move 5 from 5 to 7
move 1 from 4 to 8
move 7 from 7 to 2
move 12 from 5 to 2
move 10 from 1 to 8
move 1 from 9 to 6
move 3 from 8 to 1
move 1 from 1 to 6
move 10 from 2 to 3
move 8 from 8 to 7
move 1 from 9 to 8
move 2 from 3 to 5
move 14 from 5 to 8
move 1 from 3 to 2
move 3 from 8 to 1
move 3 from 8 to 4
move 3 from 2 to 4
move 5 from 6 to 4
move 8 from 7 to 9
move 6 from 8 to 7
move 1 from 5 to 7
move 6 from 2 to 9
move 4 from 4 to 6
move 4 from 4 to 9
move 3 from 9 to 3
move 1 from 8 to 6
move 1 from 5 to 6
move 2 from 7 to 2
move 1 from 3 to 4
move 3 from 4 to 1
move 3 from 4 to 3
move 5 from 6 to 4
move 4 from 3 to 8
move 1 from 6 to 4
move 8 from 3 to 2
move 2 from 8 to 5
move 11 from 9 to 7
move 9 from 1 to 9
move 2 from 7 to 3
move 1 from 6 to 8
move 1 from 6 to 5
move 5 from 9 to 8
move 3 from 9 to 7
move 2 from 9 to 1
move 2 from 3 to 7
move 12 from 7 to 1
move 2 from 8 to 9
move 5 from 4 to 5
move 4 from 9 to 4
move 1 from 1 to 3
move 7 from 1 to 3
move 7 from 5 to 6
move 1 from 9 to 1
move 1 from 5 to 1
move 5 from 7 to 8
move 4 from 6 to 7
move 5 from 1 to 8
move 1 from 4 to 3
move 12 from 8 to 7
move 2 from 2 to 4
move 2 from 8 to 9
move 3 from 8 to 2
move 2 from 6 to 7
move 4 from 7 to 8
move 1 from 6 to 8
move 4 from 3 to 2
move 15 from 7 to 8
move 1 from 7 to 6
move 3 from 3 to 5
move 2 from 3 to 4
move 5 from 2 to 5
move 3 from 1 to 5
move 4 from 5 to 6
move 4 from 5 to 9
move 1 from 5 to 7
move 4 from 9 to 4
move 2 from 2 to 9
move 2 from 5 to 2
move 2 from 2 to 1
move 3 from 4 to 9
move 2 from 9 to 4
move 2 from 8 to 5
move 2 from 5 to 2
move 8 from 2 to 4
move 2 from 1 to 3
move 2 from 3 to 5
move 3 from 6 to 9
move 2 from 6 to 1
move 2 from 1 to 4
move 1 from 2 to 4
move 1 from 5 to 7
move 2 from 2 to 7
move 18 from 4 to 2
move 1 from 5 to 9
move 2 from 7 to 9
move 18 from 8 to 4
move 1 from 7 to 8
move 22 from 4 to 8
move 6 from 2 to 6
move 3 from 6 to 8
move 3 from 6 to 4
move 3 from 4 to 7
move 3 from 7 to 1
move 14 from 2 to 3
move 10 from 3 to 2
move 27 from 8 to 1
move 1 from 7 to 6
move 1 from 3 to 7
move 2 from 2 to 8
move 2 from 9 to 8
move 18 from 1 to 4
move 6 from 1 to 5
move 10 from 4 to 7
move 1 from 3 to 7
move 4 from 7 to 2
move 3 from 9 to 7
move 1 from 6 to 5
move 1 from 2 to 7
move 2 from 5 to 6
move 2 from 6 to 5
move 3 from 5 to 1
move 6 from 1 to 3
move 4 from 5 to 9
move 11 from 2 to 9
move 2 from 1 to 6
move 3 from 4 to 6
move 5 from 7 to 3
move 2 from 6 to 1
move 2 from 1 to 5
move 1 from 8 to 2
move 1 from 1 to 8
move 1 from 6 to 4
move 2 from 4 to 5
move 4 from 5 to 9
move 11 from 3 to 6
move 1 from 3 to 6
move 8 from 6 to 5
move 1 from 3 to 5
move 4 from 4 to 8
move 21 from 9 to 6
move 2 from 9 to 5
move 1 from 9 to 3
move 1 from 2 to 6
move 7 from 8 to 6
move 12 from 6 to 5
move 1 from 8 to 2
move 10 from 6 to 7
move 15 from 7 to 2
move 2 from 7 to 3
move 13 from 6 to 8
move 9 from 5 to 1
move 12 from 5 to 3
move 1 from 2 to 3
move 1 from 9 to 7
move 9 from 3 to 4
move 3 from 4 to 6
move 1 from 7 to 6
move 6 from 4 to 1
move 2 from 5 to 2
move 6 from 1 to 8
move 9 from 8 to 6
move 7 from 3 to 2
move 1 from 2 to 9
move 9 from 6 to 1
move 13 from 1 to 7
move 4 from 8 to 5
move 2 from 7 to 1
move 3 from 6 to 4
move 3 from 5 to 8
move 3 from 2 to 6
move 1 from 5 to 3
move 1 from 3 to 4
move 1 from 9 to 8
move 3 from 8 to 7
move 12 from 2 to 9
move 10 from 7 to 4
move 5 from 8 to 4
move 1 from 8 to 5
move 11 from 4 to 7
move 8 from 9 to 7
move 1 from 6 to 2
move 8 from 2 to 6
move 1 from 5 to 8
move 4 from 1 to 5
move 4 from 9 to 6
move 3 from 1 to 3
move 2 from 8 to 4
move 1 from 7 to 6
move 1 from 2 to 7
move 2 from 3 to 7
move 4 from 4 to 9
move 11 from 6 to 9
move 10 from 7 to 8
move 1 from 3 to 4
move 1 from 6 to 4
move 4 from 5 to 7
move 6 from 7 to 4
move 1 from 8 to 7
move 4 from 6 to 7
move 12 from 4 to 8
move 12 from 8 to 1
move 1 from 8 to 2
move 10 from 1 to 7
move 2 from 4 to 1
move 8 from 8 to 3
move 4 from 1 to 6
move 8 from 7 to 6
move 2 from 6 to 5
move 2 from 5 to 2
move 13 from 9 to 3
move 3 from 2 to 5
move 8 from 3 to 4
move 7 from 6 to 7
move 1 from 9 to 2
move 1 from 9 to 1
move 2 from 6 to 4
move 3 from 4 to 8
move 1 from 1 to 7
move 4 from 4 to 6
move 3 from 8 to 7
move 1 from 2 to 9
move 1 from 5 to 2
move 1 from 2 to 5
move 2 from 4 to 5
move 1 from 7 to 2
move 13 from 3 to 4
move 7 from 4 to 3
move 4 from 5 to 9
move 1 from 4 to 7
move 5 from 6 to 3
move 3 from 9 to 7
move 10 from 7 to 8
move 3 from 4 to 8
move 1 from 5 to 4
move 2 from 3 to 1
move 3 from 7 to 4
move 4 from 8 to 6
move 2 from 9 to 3
move 2 from 4 to 5
move 4 from 4 to 3
move 8 from 8 to 3
move 3 from 6 to 8
move 1 from 2 to 6
move 5 from 7 to 9
move 1 from 4 to 3
move 3 from 7 to 5
move 3 from 8 to 4
move 7 from 7 to 5
move 3 from 7 to 8
move 1 from 9 to 8
move 3 from 4 to 1
move 1 from 5 to 8
move 3 from 7 to 1
move 6 from 8 to 3
move 3 from 9 to 5
move 2 from 6 to 5
move 2 from 1 to 6
move 16 from 3 to 8
move 4 from 5 to 8
move 4 from 3 to 8
move 1 from 9 to 5
move 1 from 6 to 5
move 3 from 3 to 7
move 6 from 1 to 6
move 1 from 5 to 4
move 3 from 5 to 2
move 2 from 7 to 4
move 1 from 2 to 8
move 6 from 8 to 1
move 2 from 4 to 5
move 2 from 2 to 3
move 7 from 8 to 7
move 1 from 4 to 6
move 3 from 6 to 4
move 3 from 4 to 9
move 3 from 6 to 3
move 11 from 8 to 6
move 12 from 5 to 4
move 5 from 6 to 1
move 9 from 3 to 2
move 7 from 6 to 1
move 7 from 7 to 8
move 5 from 8 to 3
move 2 from 3 to 6
move 2 from 8 to 1
move 1 from 7 to 2
move 7 from 3 to 8
move 1 from 9 to 1
move 14 from 1 to 3
move 9 from 2 to 8
move 11 from 3 to 4
move 22 from 4 to 1
move 2 from 3 to 1
move 16 from 8 to 4
move 1 from 9 to 2
move 3 from 6 to 9
move 3 from 9 to 5
move 1 from 2 to 6
move 1 from 5 to 7
"""

Part 1

[stacks, moves] =
  input
  |> String.split("\n\n")

stacks =
  stacks
  |> String.split("\n", trim: true)
  |> Enum.drop(-1)
  |> Enum.map(&String.codepoints/1)

get_stack_element_from_row = fn row, idx, stack ->
  row_idx = 4 * idx + 1
  elem = Enum.at(row, row_idx)

  if elem == " " do
    stack
  else
    [elem | stack]
  end
end

stacks =
  Enum.reduce(0..8, %{}, fn stack_idx, stack_map ->
    stack =
      stacks
      |> Enum.reduce([], &get_stack_element_from_row.(&1, stack_idx, &2))
      |> Enum.reverse()

    Map.put(stack_map, stack_idx + 1, stack)
  end)

moves =
  moves
  |> String.split("\n", trim: true)
  |> Enum.map(fn instruction ->
    instruction
    |> String.split(" ")
    |> Enum.filter(&String.match?(&1, ~r/\d+/))
    |> Enum.map(&String.to_integer/1)
    |> List.to_tuple()
  end)

Enum.reduce(moves, stacks, fn {count, from, to}, stacks ->
  for _ <- 1..count, reduce: stacks do
    acc ->
      [to_move | rest] = Map.get(acc, from)
      dest = Map.get(acc, to)

      acc
      |> Map.put(from, rest)
      |> Map.put(to, [to_move | dest])
  end
end)
|> Enum.map(fn {_, v} -> hd(v) end)

Part 2

Enum.reduce(moves, stacks, fn {count, from, to}, stacks ->
  {to_move, rest} =
    stacks
    |> Map.get(from)
    |> Enum.split(count)

  dest = Map.get(stacks, to)

  stacks
  |> Map.put(from, rest)
  |> Map.put(to, to_move ++ dest)
end)
|> Enum.map(fn {_, v} -> hd(v) end)