2023-12-08 22:21:08 -06:00
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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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2023-12-09 18:41:07 -06:00
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routes(Starts, [Route1 | RestOfRoutes]),
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foldl(unify2, RestOfRoutes, Route1, _-(_-Answer-_)).
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2023-12-08 22:21:08 -06:00
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2023-12-09 13:41:52 -06:00
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% unify2 combines 2 routes into one with its own stride-offsets-dests
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2023-12-09 18:41:07 -06:00
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unify2(Route1, Route2, NewRoute) :-
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once(findnsols(2, S, converge(Route1, Route2, S), SolutionPair)),
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SolutionPair = [NewA-LenA-NewZ, _-LenB-_],
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NewStride is LenB - LenA,
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NewRoute = NewA-(NewStride-LenA-[0-NewZ]).
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% Len = Stride1*X1 + Offset1 + Dest1 = Stride2*X2 + Offset2 + Dest2
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% For performance, Route1's Stride should =< Route2's Stride
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converge(Route1, Route2, NewA-Len-NewZ) :-
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writef('Combining %t - %t\n', [Route1, Route2]),
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2023-12-09 13:41:52 -06:00
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Route1 = A1-(Stride1-Offset1-Dests1),
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Route2 = A2-(Stride2-Offset2-Dests2),
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2023-12-09 18:41:07 -06:00
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natnum(X2),
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pick([Dests1, Dests2], [Dest1-Z1, Dest2-Z2]),
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0 is (Stride2*X2 + Offset2 + Dest2 - Offset1 - Dest1) mod Stride1,
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Len is Stride2*X2 + Offset2 + Dest2,
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atom_concat(A1, A2, NewA), atom_concat(Z1, Z2, NewZ).
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2023-12-08 22:21:08 -06:00
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routes(Starts, Routes) :-
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2023-12-09 13:41:52 -06:00
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maplist([S, S-Route]>>(zloop(S, Route)), Starts, Routes).
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2023-12-08 22:21:08 -06:00
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2023-12-09 18:41:07 -06:00
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% zloop builds a route (Stride-Offset-Internals) for a particular starting node.
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2023-12-09 13:41:52 -06:00
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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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2023-12-08 22:21:08 -06:00
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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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2023-12-09 13:41:52 -06:00
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ReversedZs, ReversedDests, Offset, _),
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reverse(ReversedDests, Dests),
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2023-12-08 22:21:08 -06:00
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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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2023-12-09 18:41:07 -06:00
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% pick([[1,2,3], [4], [5,6]], X). X = [1,4,5]; X = [1,4,6]; X = [2,4,5]; ...
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pick(ListOfLists, Items) :-
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maplist([SubList, X]>>(member(X, SubList)), ListOfLists, Items).
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natnum(0).
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natnum(N) :- natnum(N0), N is N0 + 1.
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