Day 6-2

day6.erl

@@ -3,13 +3,12 @@
 -export([solve/1]).
 
 solve(InputData) ->
-	{solve(InputData, 1), none}.
-
-solve(<<A, A, Rest/binary>>, N) -> solve(<<A, Rest/binary>>, N+1);
-solve(<<A, B, A, Rest/binary>>, N) -> solve(<<B, A, Rest/binary>>, N+1);
-solve(<<A, B, C, A, Rest/binary>>, N) -> solve(<<B, C, A, Rest/binary>>, N+1);
-solve(<<A, B, B, Rest/binary>>, N) -> solve(<<B, Rest/binary>>, N+2);
-solve(<<A, B, C, C, Rest/binary>>, N) -> solve(<<C, Rest/binary>>, N+3);
-solve(<<A, B, C, D, _Rest/binary>>, N) when A /= B andalso B /= C andalso C /= D andalso
-					    A /= C andalso B /= D andalso A /= D -> N+3;
-solve(<<_, Rest/binary>>, N) -> solve(Rest, N+1).
+	{solve2(InputData, 4), solve2(InputData, 14)}.
+
+solve2(Symbols, Target) -> solve2(Symbols, #{}, 0, 0, Target).
+
+solve2(_Symbols, _State, Target, N, Target) -> N;
+
+solve2(<<Symbol, Symbols/binary>>, LastSeen, ChainLength, N, Target) ->
+	Last = maps:get(Symbol, LastSeen, 0),
+	solve2(Symbols, LastSeen#{Symbol => N}, min(N-Last, ChainLength+1), N+1, Target).