99 lines
2.7 KiB
Perl
99 lines
2.7 KiB
Perl
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% :- table valid/1.
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:- table path/3.
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answer(Answer) :-
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pipe_at(From, ess),
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once(path(From, Via, From)),
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length(Via, ViaLen),
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writef('%t -> %t\n', [From, Via]),
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Answer is (ViaLen + 1) div 2 .
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% path(From, Next, To, Dist) :-
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% pipe_at(From, FromPipe),
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% FromG =.. [FromPipe, From, Next
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path(From, [Via], To) :-
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pipe_at(Via, ViaPipe),
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ViaG =.. [ViaPipe, Via, From, To], ViaG.
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path(From, [Via1, Via2 | Vias], To) :-
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path(From, [Via1], Via2),
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path(Via1, [Via2 | Vias], To).
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dot(_, _, _) :- fail.
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vert(X-Y, X1-Y, X2-Y) :-
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pipe_at(X-Y, vert),
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( X1 is X+1, X2 is X-1
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; X1 is X-1, X2 is X+1),
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valid(X1-Y), valid(X2-Y).
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horz(X-Y, X-Y1, X-Y2) :-
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pipe_at(X-Y, horz),
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( Y1 is Y+1, Y2 is Y-1
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; Y1 is Y-1, Y2 is Y+1),
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valid(X-Y1), valid(X-Y2).
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el(X-Y, X1-Y1, X2-Y2) :-
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pipe_at(X-Y, el),
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( Y1 = Y, X1 is X-1, Y2 is Y+1, X2 = X
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; X1 = X, Y1 is Y+1, X2 is X-1, Y2 = Y),
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valid(X1-Y1), valid(X2-Y2).
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jay(X-Y, X1-Y1, X2-Y2) :-
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pipe_at(X-Y, jay),
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( Y1 = Y, X1 is X-1, Y2 is Y-1, X2 = X
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; X1 = X, Y1 is Y-1, X2 is X-1, Y2 = Y),
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valid(X1-Y1), valid(X2-Y2).
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seven(X-Y, X1-Y1, X2-Y2) :-
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pipe_at(X-Y, seven),
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( Y1 = Y, X1 is X+1, Y2 is Y-1, X2 = X
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; X1 = X, Y1 is Y-1, X2 is X+1, Y2 = Y),
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valid(X1-Y1), valid(X2-Y2).
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eff(X-Y, X1-Y1, X2-Y2) :-
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pipe_at(X-Y, eff),
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( Y1 = Y, X1 is X+1, Y2 is Y+1, X2 = X
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; X1 = X, Y1 is Y+1, X2 is X+1, Y2 = Y),
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valid(X1-Y1), valid(X2-Y2).
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ess(X-Y, X1-Y1, X2-Y2) :-
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pipe_at(X-Y, ess),
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findall(Coord, ess_adjacent(Coord), [X1-Y1, X2-Y2]).
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ess_adjacent(X1-Y1) :-
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pipe_at(X-Y, ess),
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( X1 is X-1, Y1 = Y, pipe_at(X1-Y1, El), points_down(El)
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; X1 = X, Y1 is Y+1, pipe_at(X1-Y1, El), points_left(El)
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; X1 is X+1, Y1 = Y, pipe_at(X1-Y1, El), points_up(El)
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; X1 = X, Y1 is Y-1, pipe_at(X1-Y1, El), points_right(El)),
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valid(X1-Y1).
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points_down(El) :- (El=ess; El=vert; El=seven; El=eff).
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points_left(El) :- (El=ess; El=horz; El=jay; El=seven).
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points_up(El) :- (El=ess; El=vert; El=el; El=jay).
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points_right(El) :- (El=ess; El=horz; El=el; El=eff).
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valid(X-Y) :-
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input(Map), length(Map, NRows),
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Map = [Row0 | _], length(Row0, NCols),
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X >= 0, Y >= 0,
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X < NRows, Y < NCols.
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% Element is at (Row, Column) in the map.
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pipe_at(Row-Column, Element) :-
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input(Map),
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nth0(Row, Map, SubList),
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nth0(Column, SubList, Symbol),
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symbol_predicate(Symbol, Element).
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symbol_predicate("|", vert).
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symbol_predicate("-", horz).
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symbol_predicate("L", el).
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symbol_predicate("J", jay).
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symbol_predicate("7", seven).
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symbol_predicate("F", eff).
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symbol_predicate(".", dot).
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symbol_predicate("S", ess).
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