Advent of code - Day 5

Input

File.read!("inputs/day5.txt")
|> length()

[str_stacks, str_moves] =
  File.read!("inputs/day5.txt")
  |> String.split(" 1   2   3   4   5   6   7   8   9 ")

stacks =
  Enum.map(
    Range.new(1, 33, 4),
    fn charat ->
      str_stacks
      |> String.split("\n")
      |> Enum.map(fn s -> String.at(s, charat) end)
      |> Enum.reject(fn c -> c == nil || c == " " end)
    end
  )

indexed_stacks =
  stacks
  |> Enum.with_index(1)
  |> Enum.reduce(Map.new(), fn {v, k}, acc -> Map.put(acc, k, v) end)

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

{stacks, moves}

Partie 1

Enum.reduce(moves, stacks, fn move, stacks ->
  [amount_to_move, from_, to_] = move
  from_ = from_ - 1
  to_ = to_ - 1

  {to_remove, _} =
    stacks
    |> Enum.at(from_)
    |> Enum.split(amount_to_move)

  Range.new(0, 8)
  |> Enum.map(fn r ->
    stack = Enum.at(stacks, r)

    stack =
      if r != from_ do
        stack
      else
        Enum.drop(stack, amount_to_move)
      end

    if r != to_ do
      stack
    else
      (to_remove |> Enum.reverse()) ++ stack
    end
  end)
end)
|> Enum.map(fn s -> Enum.at(s, 0) end)
|> to_string()

Enum.reduce(moves, indexed_stacks, fn [amount_to_move, from_, to_], acc ->
  {moved, acc} = pop_in(acc, [from_, Access.slice(0..(amount_to_move - 1))])
  Map.update!(acc, to_, &(Enum.reverse(moved) ++ &1))
end)
|> Map.values()
|> Enum.map(&hd/1)
|> to_string()

Partie 2

Enum.reduce(moves, stacks, fn move, stacks ->
  [amount_to_move, from_, to_] = move
  from_ = from_ - 1
  to_ = to_ - 1

  {to_remove, _} =
    stacks
    |> Enum.at(from_)
    |> Enum.split(amount_to_move)

  Range.new(0, 8)
  |> Enum.map(fn r ->
    stack = Enum.at(stacks, r)

    stack =
      if r != from_ do
        stack
      else
        Enum.drop(stack, amount_to_move)
      end

    if r != to_ do
      stack
    else
      to_remove ++ stack
    end
  end)
end)
|> Enum.map(fn s -> Enum.at(s, 0) end)
|> to_string()

Enum.reduce(moves, indexed_stacks, fn [amount_to_move, from_, to_], acc ->
  {moved, acc} = pop_in(acc, [from_, Access.slice(0..(amount_to_move - 1))])
  Map.update!(acc, to_, &(moved ++ &1))
end)
|> Map.values()
|> Enum.map(&hd/1)
|> to_string()