Here is mine:
defmodule Aoc2024.Solutions.Y24.Day08 do
alias AoC.Input
def parse(input, _part) do
stream = Input.stream!(input, trim: true)
antennas =
stream
|> Stream.with_index()
|> Enum.reduce(%{}, fn {line, x}, antennas ->
line
|> String.to_charlist()
|> Stream.with_index()
|> Enum.reduce(antennas, fn
{?., _}, antennas -> antennas
{symbol, y}, antennas -> Map.update(antennas, symbol, [{x, y}], &[{x, y} | &1])
end)
end)
|> Map.values()
row_end = Enum.count(stream) - 1
col_end = length(String.to_charlist(Enum.at(stream, 0))) - 1
{antennas, row_end, col_end}
end
def part_one({antennas, row_end, col_end}) do
antennas
|> generate_combinations()
|> Enum.reduce(MapSet.new(), fn combinations, antinodes ->
Enum.reduce(combinations, antinodes, fn {{x1, y1}, {x2, y2}}, antinodes ->
antinodes
|> add_antinodes(x1, y1, x2 - x1, y2 - y1, row_end, col_end)
|> add_antinodes(x2, y2, x1 - x2, y1 - y2, row_end, col_end)
end)
end)
|> Enum.count()
end
def part_two({antennas, row_end, col_end}) do
antennas
|> generate_combinations()
|> Enum.reduce(MapSet.new(List.flatten(antennas)), fn combinations, antinodes ->
Enum.reduce(combinations, antinodes, fn {{x1, y1}, {x2, y2}}, antinodes ->
antinodes
|> add_antinodes_recursive(x1, y1, x2 - x1, y2 - y1, row_end, col_end)
|> add_antinodes_recursive(x2, y2, x1 - x2, y1 - y2, row_end, col_end)
end)
end)
|> Enum.count()
end
defp generate_combinations(antennas) do
for antenna <- antennas do
for {a, x} <- Enum.with_index(antenna),
{b, y} <- Enum.with_index(antenna),
x < y,
do: {a, b}
end
end
defp add_antinodes(antinodes, x_original, y_original, dx, dy, row_end, col_end) do
{x, y} = {x_original - dx, y_original - dy}
if x >= 0 and x <= row_end and y >= 0 and y <= col_end do
MapSet.put(antinodes, {x, y})
else
antinodes
end
end
defp add_antinodes_recursive(antinodes, x_original, y_original, dx, dy, row_end, col_end) do
{x, y} = {x_original - dx, y_original - dy}
if x >= 0 and x <= row_end and y >= 0 and y <= col_end do
antinodes = MapSet.put(antinodes, {x, y})
add_antinodes_recursive(antinodes, x, y, dx, dy, row_end, col_end)
else
antinodes
end
end
end
Can somebody explain to me why is part 2 faster although it’s the same kind of function for calculation as in part 1 only recursive. 
Solution for 2024 day 8
part_one: 376 in 8.85ms
part_two: 1352 in 1.22ms
I wonder what i will do rest of the year now, after december .. excercism ?
