d23p1

23/part1.pl

@@ -0,0 +1,51 @@
+:- use_module(library(pio)).
+:- use_module(library(dcg/basics)).
+:- initialization(main, main).
+
+main([FileName|_]) :-
+    input(FileName, Map),
+    nth1(1, Map, Row1), nth1(StartY, Row1, '.'),
+    findall(N, route(Map, visited{}, 1-StartY, N), Ns),
+    max_list(Ns, Answer),
+    format('~w <- ~w', [Answer, Ns]), 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, Dist),
+    NeighborKey is X1*1000 + Y1, \+ _= Visiteds.get(NeighborKey),
+    route(Map, NextVisiteds, X1-Y1, N1),
+    N is N1 + Dist.
+
+neighbor(Map, X-Y, NextX-NextY, Dist) :-
+    (   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, Cell1),
+    (   Cell1 = '.' -> NextX = X1, NextY = Y1, Dist = 1
+    ;   Cell1 = '>' -> NextX = X1, NextY is Y1 + 1, Dist = 2
+    ;   Cell1 = 'v' -> NextX is X1 + 1, NextY = Y1, Dist = 2
+    ), 
+    ( NextX =\= X; NextY =\= Y ).
+
+% 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([C|Chars]) --> [Ascii], line(Chars), {atom_codes(C, [Ascii])}.
+
+% debug
+print(Map) :-
+    findall(
+        X,
+        (   nth1(X, Map, Line),
+            format('~3d', [X]), write(" "),
+            atomic_list_concat(Line, Str), write(Str), nl
+        ),
+        _),
+    nl.