61 lines
2.0 KiB
Elixir
61 lines
2.0 KiB
Elixir
defmodule Aoc2024.Day06 do
|
|
def parse(input) do
|
|
input = input |> String.trim() |> String.split("\n") |> Enum.map(&String.codepoints/1)
|
|
w = Enum.count(Enum.at(input, 0))
|
|
h = Enum.count(input)
|
|
walk(input, w, h)
|
|
end
|
|
|
|
defp walk(t, w, h), do: walk(t, 0, 0, w, h, MapSet.new(), nil)
|
|
defp walk(_t, i, _j, w, h, walls, start) when i==h, do: {w, h, walls, start}
|
|
defp walk(t, i, j, w, h, walls, start) when j==w, do: walk(t, i+1, 0, w, h, walls, start)
|
|
defp walk(t, i, j, w, h, walls, start) do
|
|
case t |> Enum.at(i) |> Enum.at(j) do
|
|
"^" -> walk(t, i, j+1, w, h, walls, {i, j})
|
|
"#" -> walk(t, i, j+1, w, h, MapSet.put(walls, {i, j}), start)
|
|
_ -> walk(t, i, j+1, w, h, walls, start)
|
|
end
|
|
end
|
|
|
|
def part1({w, h, walls, {i, j}}) do
|
|
guard(i, j, w, h, walls)
|
|
end
|
|
defp guard(i, j, w, h, walls), do: guard(i, j, -1, 0, w, h, walls, MapSet.new())
|
|
defp guard(i, j, _, _, w, h, _, path) when i<0 or j<0 or i==h or j==w, do: path |> Enum.count()
|
|
defp guard(i, j, di, dj, w, h, walls, path) do
|
|
if MapSet.member?(walls, {i, j}) do
|
|
i = i-di
|
|
j = j-dj
|
|
{di, dj} = {dj, di}
|
|
dj = -dj
|
|
guard(i, j, di, dj, w, h, walls, path)
|
|
else
|
|
guard(i+di, j+dj, di, dj, w, h, walls, MapSet.put(path, {i, j}))
|
|
end
|
|
end
|
|
|
|
def part2({w, h, walls, {i, j}}) do
|
|
for wi <- 0..h-1, wj <- 0..w-1 do
|
|
Task.async(fn -> guard2(i, j, w, h, walls |> MapSet.put({wi, wj})) end)
|
|
end
|
|
|> Enum.map(&Task.await/1)
|
|
|> Enum.sum()
|
|
end
|
|
defp guard2(i, j, w, h, walls), do: guard2(i, j, -1, 0, w, h, walls, MapSet.new())
|
|
defp guard2(i, j, _, _, w, h, _, _) when i<0 or j<0 or i==h or j==w, do: 0
|
|
defp guard2(i, j, di, dj, w, h, walls, path) do
|
|
cond do
|
|
MapSet.member?(path, {i, j, di, dj}) ->
|
|
1
|
|
MapSet.member?(walls, {i, j}) ->
|
|
i = i-di
|
|
j = j-dj
|
|
{di, dj} = {dj, di}
|
|
dj = -dj
|
|
guard2(i, j, di, dj, w, h, walls, path)
|
|
true ->
|
|
guard2(i+di, j+dj, di, dj, w, h, walls, MapSet.put(path, {i, j, di, dj}))
|
|
end
|
|
end
|
|
end
|