day01

input = File.stream!("./2023/input_day01.txt")

Common

defmodule Undigiter do
  def parse([digit]), do: Integer.undigits([digit, digit])
  def parse([_, _] = number), do: Integer.undigits(number)

  def parse(number) do
    first = List.first(number)
    last = List.last(number)

    Integer.undigits([first, last])
  end
end

Part 01

input
|> Stream.map(&to_charlist/1)
|> Stream.map(fn line -> Enum.filter(line, &(&1 in ?0..?9)) end)
|> Stream.map(fn line -> Enum.map(line, &(&1 - ?0)) end)
|> Stream.map(&Undigiter.parse/1)
|> Enum.sum()

Part 02

digits = %{
  "1" => 1,
  "one" => 1,
  "2" => 2,
  "two" => 2,
  "3" => 3,
  "three" => 3,
  "4" => 4,
  "four" => 4,
  "5" => 5,
  "five" => 5,
  "6" => 6,
  "six" => 6,
  "7" => 7,
  "seven" => 7,
  "8" => 8,
  "eight" => 8,
  "9" => 9,
  "nine" => 9
}

regex = digits |> Map.keys() |> Enum.join("|") |> Regex.compile!()

input
|> Stream.map(fn line ->
  0..String.length(line)
  |> Enum.map(fn offset ->
    Regex.run(regex, line, capture: :first, offset: offset)
  end)
  |> List.flatten()
  |> Enum.reject(&is_nil/1)
  |> Enum.dedup()
end)
|> Stream.map(fn raw_numbers ->
  Enum.map(raw_numbers, &Map.fetch!(digits, &1))
end)
|> Stream.map(&Undigiter.parse/1)
|> Enum.sum()