Day 25-1

day25.erl

@@ -0,0 +1,31 @@
+-module(day25).
+
+-export([solve/1]).
+
+solve(Input) ->
+	RoundData = binary:split(Input, <<$\n>>, [trim_all, global]),
+    {part1(RoundData), none}.
+
+part1(Input) -> int_to_snafu(lists:sum(lists:map(fun snafu_to_int/1, Input))).
+
+snafu_to_int(Snafu) -> snafu_to_int(Snafu, 0).
+
+snafu_to_int(<<>>, Acc) -> Acc;
+snafu_to_int(<<$2, Rest/binary>>, Acc) -> snafu_to_int(Rest, Acc * 5 + 2);
+snafu_to_int(<<$1, Rest/binary>>, Acc) -> snafu_to_int(Rest, Acc * 5 + 1);
+snafu_to_int(<<$0, Rest/binary>>, Acc) -> snafu_to_int(Rest, Acc * 5);
+snafu_to_int(<<$-, Rest/binary>>, Acc) -> snafu_to_int(Rest, Acc * 5 - 1);
+snafu_to_int(<<$=, Rest/binary>>, Acc) -> snafu_to_int(Rest, Acc * 5 - 2).
+
+int_to_snafu(0) -> <<"0">>;
+int_to_snafu(N) -> int_to_snafu(N, []).
+
+int_to_snafu(0, Acc) -> list_to_binary(Acc);
+int_to_snafu(Num, Acc) ->
+    case Num rem 5 of
+        0 -> int_to_snafu(Num div 5, [$0 | Acc]);
+        1 -> int_to_snafu(Num div 5, [$1 | Acc]);
+        2 -> int_to_snafu(Num div 5, [$2 | Acc]);
+        3 -> int_to_snafu(Num div 5 + 1, [$= | Acc]);
+        4 -> int_to_snafu(Num div 5 + 1, [$- | Acc])
+    end.