day8

day7.pl

@@ -81,4 +81,3 @@ part2(File) :-
   writeln(R), !.
 
 % vim: set ft=prolog :
-% vim what the fuck is "gringo"

day8.pl

@@ -0,0 +1,61 @@
+:- use_module(library(dcg/basics)).
+
+direction(left)  --> "L".
+direction(right) --> "R".
+
+directions([])     --> [].
+directions([D|Ds]) --> direction(D), directions(Ds).
+
+label(L) -->
+  alpha_to_lower(A), alpha_to_lower(B), alpha_to_lower(C),
+  {atom_codes(L, [A,B,C])}.
+
+line(A-B-C) -->
+  label(A), blanks, "=", blanks, "(", label(B), ",", blanks, label(C), ")".
+
+lines([])     --> blanks.
+lines([L|Ls]) --> line(L), blanks, lines(Ls).
+
+file(Ds, Ls) --> directions(Ds), blanks, lines(Ls).
+
+set_map(Map) :- reset_map, maplist(assert_map1, Map).
+reset_map :- abolish(left/2), abolish(right/2).
+assert_map1(A-B-C) :- assertz(left(A, B)), assertz(right(A, C)).
+:- dynamic left/2, right/2.
+
+loop_with(P, N, N, _, _, Z) :- call(P, Z), !.
+loop_with(P, N, I, [D|Ds], All, Here) :-
+  call(D, Here, Next),
+  I1 is I + 1,
+  loop_with(P, N, I1, Ds, All, Next).
+loop_with(P, N, I, [], All, Here) :-
+  loop_with(P, N, I, All, All, Here).
+
+go(N, Ds) :- loop_with(=(zzz), N, 0, Ds, Ds, aaa).
+
+part1(File) :-
+  phrase_from_file(file(Ds, Map), File),
+  set_map(Map),
+  go(N, Ds),
+  writeln(N).
+
+
+is_start(S) :- atom_chars(S, [_, _, a]).
+is_final(S) :- atom_chars(S, [_, _, z]).
+
+starts(Xs) :- setof(X, Y^(left(X, Y), is_start(X)), Xs).
+
+loop_multi(Ds, Here, N) :- loop_with(is_final, N, 0, Ds, Ds, Here).
+
+go_multi(Ns, Ds) :- starts(Ss), maplist(loop_multi(Ds), Ss, Ns).
+
+lcm(M, N, L) :- L is lcm(M, N).
+
+part2(File) :-
+  phrase_from_file(file(Ds, Map), File),
+  set_map(Map),
+  go_multi(Ns, Ds),
+  foldl(lcm, Ns, 1, N),
+  writeln(N).
+
+% vim: set ft=prolog :