Day 6: Trash Compactor

Day 6: Trash Compactor

Day 6: Trash Compactor

Part 1

defmodule AdventOfCode2025Day6Part1 do
  def run(input) do
    input
    |> parse_input()
    |> solve()
  end

  defp solve({operations, list_of_lists}) do
    0..(Enum.count(operations) - 1)
    |> Enum.reduce(0, fn i, acc ->
      numbers = 0..(Enum.count(list_of_lists) - 1)
      |> Enum.map(fn j ->
        list_of_lists |> Enum.at(j) |> Enum.at(i)
      end)

      if Enum.at(operations, i) == "+" do
        Enum.sum(numbers) + acc
      else
        Enum.product(numbers) + acc
      end
    end)
  end

  defp parse_input(input) do
    [operations | numbers] = input
    |> String.split("\n", trim: true)
    |> Enum.reverse()

    operations = String.split(operations, " ", trim: true)

    list_of_lists = Enum.reduce(numbers, [], fn line, acc ->
      list = line
      |> String.split(" ", trim: true)
      |> Enum.map(&String.to_integer/1)

      [list | acc]
    end)

    {operations, list_of_lists}
  end
end

input = """
123 328  51 64 
 45 64  387 23 
  6 98  215 314
*   +   *   +  
"""

AdventOfCode2025Day6Part1.run(input)

Part 2

defmodule AdventOfCode2025Day6Part2 do
  def run(input) do
    input
    |> parse_input()
    |> solve()
  end

  defp solve({operations, list_of_lists}) do
    Enum.zip(operations, list_of_lists)
    |> Enum.reduce(0, fn 
      {"*", list}, acc -> acc + Enum.product(list)
      {"+", list}, acc -> acc + Enum.sum(list)
    end)
  end

  defp parse_input(input) do
    [operations | numbers] = input
    |> String.split("\n", trim: true)
    |> Enum.reverse()

    operations = String.split(operations, " ", trim: true)

    list_of_charlists = numbers |> Enum.reverse() |> Enum.map(&String.to_charlist/1)
    width = Enum.at(list_of_charlists, 0) |> Enum.count()
    height = Enum.count(list_of_charlists)

    last_index = Enum.count(operations) - 1
    {list_of_lists, [], list, ^last_index} = 
    for i <- 0..(width - 1), j <- 0..(height - 1) do
      {j, i}
    end
    |> Enum.reduce({[], [], [], 0}, fn {j, i}, {list_of_lists, tmp, acc, index} ->
      v = Enum.at(list_of_charlists, j) |> Enum.at(i)
      new_tmp = [v | tmp]
      if j >= height - 1 do
        if Enum.all?(new_tmp, &amp; &amp;1 == 0x20) do
          new_list_of_lists = List.insert_at(list_of_lists, index, acc)
          {new_list_of_lists, [], [], index + 1}
        else
          num = new_tmp |> Enum.filter(&amp; &amp;1 != 0x20) |> Enum.reverse() |> List.to_integer()
          new_acc = [num | acc]
          {list_of_lists, [], new_acc, index}
        end
      else
        {list_of_lists, new_tmp, acc, index}
      end
    end)

    {operations, List.insert_at(list_of_lists, last_index, list)}
  end
end

input = """
123 328  51 64 
 45 64  387 23 
  6 98  215 314
*   +   *   +  
"""

AdventOfCode2025Day6Part2.run(input)