Day 3-1

day3.erl

@@ -0,0 +1,22 @@
+-module(day3).
+
+-export([solve/1]).
+
+solve(InputData) ->
+	Rucksacks = binary:split(InputData, <<$\n>>, [trim_all, global]),
+	{lists:foldl(fun asdf/2, 0, Rucksacks), none}.
+
+asdf(Rucksack, TotalPriority) ->
+	CompartmentSize = byte_size(Rucksack) div 2,
+	<<Compartment1:CompartmentSize/binary, Compartment2:CompartmentSize/binary>> = Rucksack,
+	[DupeLetter] = maps:keys(sets:intersection(tally(Compartment1), tally(Compartment2))),
+	priority(DupeLetter) + TotalPriority.
+
+tally(Compartment) -> tally(Compartment, #{}).
+tally(<<>>, Set) -> Set;
+tally(<<Item, Rest/binary>>, Set) when is_map_key(Item, Set) -> tally(Rest, Set);
+tally(<<Item, Rest/binary>>, Set) -> tally(Rest, Set#{Item => []}).
+
+priority(Item) when Item >= $a andalso Item =< $z -> Item - $a + 1;
+priority(Item) when Item >= $A andalso Item =< $Z -> Item - $A + 27.
+