84 lines
3.0 KiB
Perl
84 lines
3.0 KiB
Perl
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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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writef('Collapsing: %t\n', [Routes]),
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sort(2, @=<, Routes, [Route1, Route2 | CdrRoutes]),
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unify2(Route1, Route2, NewRoute),
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collapse_routes([NewRoute | CdrRoutes], Collapsed).
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% unify2 combines 2 routes into one with its own stride-offsets-dests
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unify2(Route1, Route2, Route12) :- unify2(Route1, Route2, 0-0-0-0, [], Route12).
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unify2(Route1, Route2, N1-Dest1-N2-Dest2, Founds, NewRoute) :-
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Route1 = A1-(Stride1-Offset1-Dests1),
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Route2 = A2-(Stride2-Offset2-Dests2),
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nth0(Dest1, Dests1, C1-Z1),
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nth0(Dest2, Dests2, C2-Z2),
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Len1 is Offset1 + Stride1*N1 + C1,
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Len2 is Offset2 + Stride2*N2 + C2,
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next(Dests1, N1-Dest1, NextN1-NextDest1),
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( Len1 =:= Len2
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-> ( Founds = [OldLen]
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-> atom_concat(A1, A2, NewA), atom_concat(Z1, Z2, NewZ),
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NewStride is Len1 - OldLen,
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NewRoute = NewA-(NewStride-OldLen-[0-NewZ]),
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!
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; unify2(Route1, Route2, NextN1-NextDest1-N2-Dest2, [Len1], NewRoute)
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)
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; Len1 < Len2
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-> unify2(Route1, Route2, NextN1-NextDest1-N2-Dest2, Founds, NewRoute)
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; next(Dests2, N2-Dest2, NextN2-NextDest2),
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unify2(Route1, Route2, N1-Dest1-NextN2-NextDest2, Founds, NewRoute)
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).
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% next(Dests, NumberOfLoops-WhichInternalZ, NextNumberOfLoops-NextInternalZ)
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next(Dests, NLoops-Dest, NextNLoops-NextDest) :-
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length(Dests, DestsLen),
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( Dest < DestsLen - 1
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-> NextNLoops is NLoops, NextDest is Dest + 1
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; NextNLoops is NLoops + 1, NextDest is 0).
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routes(Starts, Routes) :-
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maplist([S, S-Route]>>(zloop(S, Route)), Starts, Routes).
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% zloop builds a route (Stride-Offset-Internals for a particular starting node.
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zloop(Node, Route) :- zloop([], Node, 0, [], Route).
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zloop(_Direction, _Node, _Index, Zs, Stride-Offset-Dests) :-
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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, ReversedDests, Offset, _),
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reverse(ReversedDests, Dests),
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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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