Day 3

Day 3: Gear Ratios

Day 3: Gear Ratios

Input

input = """
467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..
"""

Part 1

input = """
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"""

[head | tail] =
  input
  |> String.split("\n", trim: true)
  |> Enum.map(&String.to_charlist/1)

x_count = Enum.count(head)
y_count = Enum.count(tail) + 1
list_of_lists = [head | tail]

map =
  for y <- 0..(y_count - 1), x <- 0..(x_count - 1), into: %{} do
    {{x, y}, Enum.at(list_of_lists, y) |> Enum.at(x)}
  end

f_is_number = fn x -> x in ?0..?9 end
f_is_symbol = fn x -> !f_is_number.(x) and x != ?. end

f_is_adjacent_to_a_symbol = fn {x, y} ->
  Map.get(map, {x, y - 1}, ?0) |> f_is_symbol.() or
    Map.get(map, {x + 1, y - 1}, ?0) |> f_is_symbol.() or
    Map.get(map, {x + 1, y}, ?0) |> f_is_symbol.() or
    Map.get(map, {x + 1, y + 1}, ?0) |> f_is_symbol.() or
    Map.get(map, {x, y + 1}, ?0) |> f_is_symbol.() or
    Map.get(map, {x - 1, y + 1}, ?0) |> f_is_symbol.() or
    Map.get(map, {x - 1, y}, ?0) |> f_is_symbol.() or
    Map.get(map, {x - 1, y - 1}, ?0) |> f_is_symbol.()
end

0..(y_count - 1)
|> Enum.reduce([], fn y, acc ->
  0..(x_count - 1)
  |> Enum.reduce({[], [], false}, fn x, {acc, tmp, adjacent} ->
    num = Map.get(map, {x, y})

    if x == x_count - 1 do
      if f_is_number.(num) do
        if adjacent do
          new_num = List.insert_at(tmp, -1, num - ?0) |> Enum.join() |> String.to_integer()
          {[new_num | acc], [], false}
        else
          adjacent = f_is_adjacent_to_a_symbol.({x, y})

          if adjacent do
            new_num = List.insert_at(tmp, -1, num - ?0) |> Enum.join() |> String.to_integer()
            {[new_num | acc], [], false}
          else
            {acc, [], false}
          end
        end
      else
        if adjacent do
          new_num = tmp |> Enum.join() |> String.to_integer()
          {[new_num | acc], [], false}
        else
          {acc, [], false}
        end
      end
    else
      if f_is_number.(num) do
        if adjacent do
          {acc, List.insert_at(tmp, -1, num - ?0), adjacent}
        else
          {acc, List.insert_at(tmp, -1, num - ?0), f_is_adjacent_to_a_symbol.({x, y})}
        end
      else
        if adjacent do
          new_num = tmp |> Enum.join() |> String.to_integer()
          {[new_num | acc], [], false}
        else
          {acc, [], false}
        end
      end
    end
  end)
  |> elem(0)
  |> Kernel.++(acc)
end)
|> Enum.sum()

f_is_adjacent_to_a_symbol.({10, 1})

Part 2