81 lines
2.6 KiB
Perl
81 lines
2.6 KiB
Perl
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:- table direction_loop/1.
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:- op(700, xfx, l).
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:- op(700, xfx, r).
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From l To :- From to To-_.
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From r To :- From to _-To.
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answer(Answer) :-
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starts(Starts),
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routes(Starts, Routes),
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collapse_routes(Routes, _-(Answer-_-_)).
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collapse_routes([X], X).
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collapse_routes(Routes, Collapsed) :-
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sort(2, @=<, Routes, [Route1, Route2 | CdrRoutes]),
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unify2(Route1, Route2, 0-0-0-0, [], NewRoute),
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collapse_routes([NewRoute | CdrRoutes], Collapsed).
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unify2(Route1, Route2, N1-Term1-N2-Term2, Founds, NewRoute) :-
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Route1 = A1-(Stride1-Offset1-Loop1),
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Route2 = A2-(Stride2-Offset2-Loop2),
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nth0(Term1, Loop1, C1-_),
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nth0(Term2, Loop2, C2-_),
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Z1 is Offset1 + Stride1*N1 + C1,
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Z2 is Offset2 + Stride2*N2 + C2,
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next(Route1, N1-Term1, NextN1-NextTerm1),
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( Z1 =:= Z2
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-> ( Founds = [OldZ]
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-> atom_concat(A1, A2, NewA),
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NewStride is Z1 - OldZ,
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NewRoute = NewA-(NewStride-OldZ-[0-NewA]),
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!
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; unify2(Route1, Route2, NextN1-NextTerm1-N2-Term2, [Z1], NewRoute)
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)
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; Z1 < Z2
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-> unify2(Route1, Route2, NextN1-NextTerm1-N2-Term2, Founds, NewRoute)
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; next(Route2, N2-Term2, NextN2-NextTerm2),
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unify2(Route1, Route2, N1-Term1-NextN2-NextTerm2, Founds, NewRoute)
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).
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next(_-(_-_-Loop), NLoops-Term, NextNLoops-NextTerm) :-
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length(Loop, LoopLen),
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( Term < LoopLen - 1
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-> NextNLoops is NLoops, NextTerm is Term + 1
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; NextNLoops is NLoops + 1, NextTerm is 0).
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routes(Starts, Routes) :-
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maplist([S, S-Route]>>(zloop([], S, 0, [], Route)), Starts, Routes).
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zloop(_, _, _, Zs, Stride-Offset-Loop) :-
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Zs = [FirstZIndex-Z | _], reverse(Zs, [LastZIndex-Z | ReversedZs]),
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DeltaZ is LastZIndex - FirstZIndex, DeltaZ =\= 0,
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direction_len(Len),
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divmod(DeltaZ, Len, _, 0),
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Offset = FirstZIndex, Stride = DeltaZ,
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foldl([Idx-Z, NewIdx-Z, Off, Off]>>(NewIdx is Idx - Off),
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ReversedZs, ReversedLoop, Offset, _),
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reverse(ReversedLoop, Loop),
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!.
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zloop(Directions, Node, Index, Zs, Route) :-
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( is_end(Node)
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-> append(Zs, [Index-Node], NewZs)
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; NewZs = Zs
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),
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next_step(Directions, Move, Remain),
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G =.. [Move, Node, To], G,
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NewIndex is Index + 1,
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zloop(Remain, To, NewIndex, NewZs, Route).
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starts(Starts) :- findall(X, X to _, Nodes), include(is_start, Nodes, Starts).
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is_start(Node) :- atom_chars(Node, [_, _, a]).
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is_end(Node) :- atom_chars(Node, [_, _, z]).
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next_step([Move | Remain], Move, Remain).
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next_step([], Move, Remain) :- direction_list([Move | Remain]).
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direction_list(Dir) :- direction(Str), atom_chars(Str, Dir).
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direction_len(Len) :- direction_list(D), length(D, Len).
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