Day 2: Red-Nosed Reports

Mix.install([:kino])

input = Kino.Input.textarea("Please paste your input:")

Part 1

https://adventofcode.com/2024/day/2

data =
  input
  |> Kino.Input.read()
  |> String.split("\n", trim: true)

reports =
  data
  |> Enum.map(fn line -> String.split(line) |> Enum.map(&String.to_integer/1) end)

check_fun = fn report ->
  report
  |> Enum.chunk_every(2, 1, :discard)
  |> Enum.reduce_while(_diff = 0, fn [num0, num1], prev_diff ->
    diff = num0 - num1

    with true <- abs(diff) >= 1,
         true <- abs(diff) <= 3,
         true <- diff * prev_diff >= 0 do
      {:cont, diff}
    else
      _ -> {:halt, false}
    end
  end)
  |> case do
    false -> false
    _ -> true
  end
end

reports
|> Enum.map(check_fun)
|> Enum.count(&amp;(&amp;1 == true))

Part 2

https://adventofcode.com/2024/day/2#part2

remove_each_el_fun = fn
  {_, []}, acc, _recur ->
    acc

  {f, [bt | br]}, acc, recur ->
    new_acc = [f ++ br | acc]
    recur.({f ++ [bt], br}, new_acc, recur)
end

reports
|> Enum.map(fn report ->
  candidates = [report | remove_each_el_fun.({[], report}, [], remove_each_el_fun)]

  candidates
  |> Stream.map(check_fun)
  |> Enum.any?()
end)
|> Enum.count(&(&1 == true))