Advent of Code Day 8 Part 1 and Part 2

aoc_8.erl

-module(aoc).

-export([main/1]).

main([Path]) ->
  {ok, Content} = file:read_file(Path),
  {Nodes, Max} = nodes(Content, 0, 0, {0,0}, #{}),
  Anti = maps:fold(fun(_, L, S) ->
    antinodes(L, L, Max, S)
  end, sets:new(), Nodes),
  io:format("~p~n", [sets:size(Anti)]),
  erlang:halt(0).

nodes(<<>>, _, _, Max, Map) -> {Map, Max};
nodes(<<"\n", T/binary>>, Y, _, {MX,MY}, Map) ->
  nodes(T, Y+1, 0, {max(MX, 0), max(MY, Y+1)}, Map);
nodes(<<".", T/binary>>, Y, X, {MX,MY}, Map) ->
  nodes(T, Y, X+1, {max(MX, X), max(MY, Y)}, Map);
nodes(<<C:1/binary, T/binary>>, Y, X, {MX,MY}, Map) ->
  Map1 = maps:update_with(C, fun(L) -> [{X,Y} | L] end, [{X,Y}], Map),
  nodes(T, Y, X+1, {max(MX, X), max(MY, Y)}, Map1).

antinodes(L, N, Max, S0) ->
  lists:foldl(fun(H, S1) ->
    {[P0], R} = lists:partition(fun(E) -> E == H end, N),
    lists:foldl(fun(P1, S2) ->
      antinode(P0, P1, Max, sets:add_element(P1, S2))
    end, S1, R)
  end, S0, L).

antinode({X1,Y1}, {X2,Y2}=P1, {MaxX,MaxY}=B, S) ->
  A = {X,Y} = {X2-(X1-X2),Y2-(Y1-Y2)},
  if
    X >= 0, X =< MaxX, Y >= 0, Y =< MaxY ->
      antinode(P1, A, B, sets:add_element(A, S));
    true -> S
  end.