day 9 solution

day9/Makefile

@@ -0,0 +1,8 @@
+all: day9.beam
+	erl -noshell -s day9 start -s init stop
+
+day9.beam:
+	erlc day9.erl
+
+clean:
+	rm -f day9.beam

day9/day9.erl

@@ -0,0 +1,37 @@
+-module(day9).
+-export([start/0]).
+
+calc_group_score(String)
+  -> calc_group_score(re:split(String, ""), 0, false, 0, false, 0).
+calc_group_score([<<>>], Score, _LastCharWasEx, _Depth, _FoundGarbage, CharCount)
+  -> {Score, CharCount};
+%calc_group_score(List, Score, LastCharWasEx, Depth, FoundGarbage, CharCount)
+%  when Score < 0 -> calc_group_score(List, 0, LastCharWasEx, Depth, FoundGarbage, CharCount);
+calc_group_score([_Head|Tail], Score, LastCharWasEx, Depth, FoundGarbage, CharCount)
+  when LastCharWasEx == true, FoundGarbage == true -> calc_group_score(Tail, Score, false, Depth, true, CharCount);
+calc_group_score([Head|Tail], Score, _LastCharWasEx, Depth, FoundGarbage, CharCount)
+  when Head == <<"!">> -> calc_group_score(Tail, Score, true, Depth, FoundGarbage, CharCount);
+calc_group_score([Head|Tail], Score, _LastCharWasEx, Depth, FoundGarbage, CharCount)
+  when Head == <<"{">>, FoundGarbage == false -> calc_group_score(Tail, Score, false, Depth + 1, false, CharCount);
+calc_group_score([Head|Tail], Score, _LastCharWasEx, Depth, FoundGarbage, CharCount)
+  when Head == <<"}">>, FoundGarbage == false -> calc_group_score(Tail, Score + Depth, false, Depth - 1, false, CharCount);
+calc_group_score([Head|Tail], Score, _LastCharWasEx, Depth, FoundGarbage, CharCount)
+  when Head == <<"<">>, FoundGarbage == false -> calc_group_score(Tail, Score, false, Depth, true, CharCount);
+calc_group_score([Head|Tail], Score, _LastCharWasEx, Depth, _FoundGarbage, CharCount)
+  when Head == <<">">> -> calc_group_score(Tail, Score, false, Depth, false, CharCount);
+calc_group_score([_Head|Tail], Score, _LastCharWasEx, Depth, FoundGarbage, CharCount)
+  when FoundGarbage == true -> calc_group_score(Tail, Score, false, Depth, FoundGarbage, CharCount + 1);
+calc_group_score([_Head|Tail], Score, _LastCharWasEx, Depth, FoundGarbage, CharCount)
+  -> calc_group_score(Tail, Score, false, Depth, FoundGarbage, CharCount).
+
+start()
+  -> io:fwrite("~p~n", [calc_group_score("{}")]),
+     io:fwrite("~p~n", [calc_group_score("{{{}}}")]),
+     io:fwrite("~p~n", [calc_group_score("{{},{}}")]),
+     io:fwrite("~p~n", [calc_group_score("{{{},{},{{}}}}")]),
+     io:fwrite("~p~n", [calc_group_score("{<a>,<a>,<a>,<a>}")]),
+     io:fwrite("~p~n", [calc_group_score("{{<ab>},{<ab>},{<ab>},{<ab>}}")]),
+     io:fwrite("~p~n", [calc_group_score("{{<!!>},{<!!>},{<!!>},{<!!>}}")]),
+     io:fwrite("~p~n", [calc_group_score("{{<a!>},{<a!>},{<a!>},{<ab>}}")]),
+     {ok, File} = file:read_file("input"),
+     io:fwrite("~p~n", [calc_group_score(unicode:characters_to_list(File))]).