Day 13-2

day13.erl

@@ -2,12 +2,10 @@
 
 -export([solve/1]).
 
--compile(export_all).
-
 solve(Input) ->
     PacketPairs = binary:split(Input, <<"\n\n">>, [global, trim_all]),
     Part1 = part1(PacketPairs),
-    {Part1, none}.
+    {Part1, part2(Input)}.
 
 part1(PacketPairs) -> part1(PacketPairs, {1, 0}).
 
@@ -22,6 +20,19 @@ part1([PacketPair|Rest], {Index, Score}) ->
                end,
     part1(Rest, {Index+1, NewScore}).
 
+part2(Input) ->
+    Packets0 = binary:split(Input, <<"\n">>, [global, trim_all]),
+    Packets1 = lists:filter(fun(X) -> byte_size(X) > 0 end, Packets0),
+    Packets2 = lists:map(fun parse_packet/1, Packets1),
+    Packets3 = [[[2]], [[6]] | Packets2], % add signal packets
+    Packets = lists:sort(fun compare/2, Packets3),
+    find([[2]], Packets) * find([[6]], Packets).
+
+find(Item, List) -> find(Item, List, 1).
+find(_Item, [], _Index) -> 0;
+find(Item, [Item | _Rest], Index) -> Index;
+find(Item, [_Head | Rest], Index) -> find(Item, Rest, Index+1).
+
 compare([], []) -> undecided;
 compare([], [_|_Rest]) -> true;
 compare([_|_Rest], []) -> false;