From 336dc780c8d2b84ddd2cdf13ceb7d4a4c2a4231f Mon Sep 17 00:00:00 2001
From: Shanti Chellaram <shanti@shanti.im>
Date: Sat, 3 Dec 2022 15:39:35 +0900
Subject: [PATCH] Day 3-1

---
 day3.erl | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 day3.erl

diff --git a/day3.erl b/day3.erl
new file mode 100644
index 0000000..81fffac
--- /dev/null
+++ b/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.
+