d18p2

18/part2.pl

@@ -0,0 +1,31 @@
+:- use_module(library(pio)).
+:- use_module(library(dcg/basics)).
+:- initialization(main, main).
+
+main([FileName|_]) :-
+    input(FileName, Moves),
+    area(Moves, Area),
+    write(Area), nl.
+
+area(Moves, Area) :-
+    area(Moves, 0, A1), MainArea is abs(A1),
+    convlist([r-N, N]>>(true), Moves, Horzs), sum_list(Horzs, Horz),
+    convlist([u-N, N]>>(true), Moves, Verts), sum_list(Verts, Vert),
+    Area is MainArea + Horz + Vert + 1.
+
+area([], _, 0).
+area([u-Len|Moves], H, Area) :- NewH is H + Len, area(Moves, NewH, Area).
+area([d-Len|Moves], H, Area) :- NewH is H - Len, area(Moves, NewH, Area).
+area([r-Len|Moves], H, Area) :- area(Moves, H, Area2), Area is Area2 + H*Len.
+area([l-Len|Moves], H, Area) :- area(Moves, H, Area2), Area is Area2 - H*Len.
+
+input(FileName, Moves) :- phrase_from_file(moves(Moves), FileName).
+moves([]) --> eos, !.
+moves([Move|Moves]) --> move(Move), moves(Moves).
+move(DirAtom-Len) -->
+    alpha_to_lower(_), " ", number(_), " (#", xinteger(Hex), ")", ("\n"; eos),
+    {DirNum is Hex /\ 15, dir(DirNum, DirAtom), Len is Hex >> 4}.
+dir(0, r).
+dir(1, d).
+dir(2, l).
+dir(3, u).