Advent of Code 2023 Day 3

Mix.install([
  {:kino_aoc, "~> 0.1.5"}
])

Section

{:ok, puzzle_input} =
  KinoAOC.download_puzzle("2023", "3", System.fetch_env!("LB_AOC_SESSION"))

lines = String.split(puzzle_input, "\n") |> Enum.with_index()

nums =
  lines
  |> Enum.flat_map(fn {line, i} ->
    Regex.scan(~r/\d+/, line, return: :index)
    |> List.flatten()
    |> Enum.map(fn {j, len} ->
      {(i - 1)..(i + 1)//1, (j - 1)..(j + len)//1, String.to_integer(String.slice(line, j, len))}
    end)
  end)

Part 1

symbol_positions =
  lines
  |> Stream.flat_map(fn {line, i} ->
    Regex.scan(~r/[^a-zA-Z0-9\.]/, line, return: :index)
    |> List.flatten()
    |> Enum.map(fn {j, _} -> {i, j} end)
  end)
  |> MapSet.new()

nums
|> Stream.filter(fn {row_span, col_span, _n} ->
  for i <- row_span,
      j <- col_span,
      reduce: false,
      do: (acc -> acc || {i, j} in symbol_positions)
end)
|> Stream.map(&elem(&1, 2))
|> Enum.sum()

Part 2

lines
|> Stream.flat_map(fn {line, i} ->
  Regex.scan(~r/\*/, line, return: :index)
  |> List.flatten()
  |> Enum.map(fn {j, _} -> {i, j} end)
end)
|> Stream.map(fn {i, j} ->
  case Enum.filter(nums, fn {row_span, col_span, _n} -> i in row_span and j in col_span end) do
    [a, b] -> elem(a, 2) * elem(b, 2)
    _ -> 0
  end
end)
|> Enum.sum()