🎄 Year 2022 🔔 Day 08

Problem

Parse input

filename = "#{__DIR__}/../../../inputs/2022/day08.txt"

left_to_right =
  File.stream!(filename)
  |> Enum.map(&String.trim(&1, "\n"))
  |> Enum.map(fn line -> line |> String.graphemes() |> Enum.map(&String.to_integer/1) end)
  |> Enum.with_index(fn line, y ->
    Enum.with_index(line, fn e, x -> {{x, y}, e} end)
  end)

right_to_left = left_to_right |> Enum.map(&Enum.reverse/1)
top_to_bottom = left_to_right |> List.zip() |> Enum.map(&Tuple.to_list/1)
bottom_to_top = top_to_bottom |> Enum.map(&Enum.reverse/1)

max_y = left_to_right |> Enum.count() |> then(&(&1 - 1))
max_x = top_to_bottom |> Enum.count() |> then(&(&1 - 1))

Shared code

Part One

Enum.concat([left_to_right, right_to_left, top_to_bottom, bottom_to_top])
|> Enum.flat_map(fn [head | tail] ->
  Enum.reduce_while(tail, [head], fn e = {_, h}, acc = [{_, max_h} | _] ->
    cond do
      max_h == 9 ->
        {:halt, acc}

      h > max_h ->
        {:cont, [e | acc]}

      true ->
        {:cont, acc}
    end
  end)
end)
|> Enum.uniq()
|> Enum.count()

Part two

defmodule Helper do
  def take_until(list, func) do
    list
    |> Enum.reduce_while([], fn e, acc ->
      if func.(e), do: {:cont, [e | acc]}, else: {:halt, [e | acc]}
    end)
    |> Enum.reverse()
  end
end

Enum.concat([left_to_right, right_to_left, top_to_bottom, bottom_to_top])
|> Enum.flat_map(&Enum.scan(&1, [], fn e, acc -> [e | acc] end))
|> Enum.reduce(%{}, fn [{coord, head} | tail], tree_map ->
  if tail != [] do
    distance = Helper.take_until(tail, fn {_, e} -> e < head end) |> Enum.count()

    tree_map |> Map.update(coord, distance, &amp;(&amp;1 * distance))
  else
    tree_map |> Map.put(coord, 0)
  end
end)
|> Enum.map(&amp;elem(&amp;1, 1))
|> Enum.max()