d8

08/part2.naive.pl

@@ -0,0 +1,25 @@
+:- op(700, xfx, l).
+:- op(700, xfx, r).
+
+From l To :- From to To-_.
+From r To :- From to _-To.
+
+answer(Answer) :- starts(Starts), path([], Starts, Answer).
+
+path(_, EndNodes, []) :- all_ends(EndNodes), !.
+path(Directions, FromList, Moves) :-
+    next_step(Directions, Move, Remain),
+    maplist(Move, FromList, ToList),
+    path(Remain, ToList, RemainingMoves),
+    Moves is RemainingMoves + 1.
+
+next_step([Move | Remain], Move, Remain).
+next_step([], Move, Remain) :- direction(Str), atom_chars(Str, [Move | Remain]).
+
+starts(StartNodes) :-
+    findall(Node, Node to _, Nodes),
+    include(is_start, Nodes, StartNodes).
+all_ends(Nodes) :- maplist(is_end, Nodes).
+
+is_start(Node) :- atom_chars(Node, [_, _, a]).
+is_end(Node) :- atom_chars(Node, [_, _, z]).