d23p2 naive

23/part2.pl

@@ -0,0 +1,51 @@
+:- use_module(library(pio)).
+:- use_module(library(dcg/basics)).
+:- initialization(main, main).
+:- table neighbor/3.
+
+main([FileName|_]) :-
+    input(FileName, Map),
+    nth1(1, Map, Row1), nth1(StartY, Row1, '.'),
+    findall(
+        N,
+        (route(Map, visited{}, 1-StartY, N), format('~w, ', [N]), flush_output),
+        Ns),
+    max_list(Ns, Answer),
+    nl, format('Answer = ~w', [Answer]), nl.
+
+route(Map, _, X-_, 0) :- length(Map, Height), X =:= Height.
+route(Map, Visiteds, X-Y, N) :-
+    Key is X*1000 + Y, NextVisiteds = Visiteds.put(Key, true),
+    neighbor(Map, X-Y, X1-Y1),
+    NeighborKey is X1*1000 + Y1, \+ _= Visiteds.get(NeighborKey),
+    route(Map, NextVisiteds, X1-Y1, N1),
+    N is N1 + 1.
+
+neighbor(Map, X-Y, X1-Y1) :-
+    (   X1 is X + 1, Y1 = Y;
+        X1 is X - 1, Y1 = Y;
+        X1 = X, Y1 is Y + 1;
+        X1 = X, Y1 is Y - 1
+    ),
+    nth1(X1, Map, Row1), nth1(Y1, Row1, '.').
+
+% input parsing stuff below. Brick indexing is for debugging.
+input(FileName, Map) :- phrase_from_file(lines(Map), FileName).
+
+lines([]) --> eos, !.
+lines([Line|Lines]) --> line(Line), lines(Lines).
+
+line([]) --> ("\n"; eos), !.
+line(['#'|Chars]) --> "#", line(Chars).
+line(['.'|Chars]) --> ("."; ">"; "v"), line(Chars).
+
+% debug
+print(Map) :-
+    findall(
+        X,
+        (   nth1(X, Map, Line),
+            format('~3d', [X]), write(" "),
+            atomic_list_concat(Line, Str), write(Str), nl
+        ),
+        _),
+    nl.