79 lines
2.9 KiB
Prolog
79 lines
2.9 KiB
Prolog
:- 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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maplist([S, S-Off-Stride-Loop]>>(zloop([], S, 0, [], Off, Stride, Loop)),
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Starts, Events),
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maplist([Node, Node-0-0]>>(true), Starts, StartPositions),
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next_zevent(Events, StartPositions, Answer).
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next_zevent(AllZEvents, CurrPositions, Index) :-
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maplist(index_of, AllZEvents, CurrPositions, Candidates),
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writef('curr=%t, cand=%t, idx=%t\n', [CurrPositions, Candidates, Index]),
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( same_elements(Candidates)
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-> Candidates = [Index-_ | _]
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; min_member(_-Z, Candidates),
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member(Z-NLoops-SubLoop, CurrPositions),
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member(Z-Offset-Stride-Loop, AllZEvents),
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next(Z-Offset-Stride-Loop, Z-NLoops-SubLoop, Z-NextNLoops-NextSubLoop),
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select(Z-_-_, CurrPositions, Z-NextNLoops-NextSubLoop, NextPositions),
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% writef('next=%t, z=%t, idx=%t\n', [NextPositions, Z, Index]),
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next_zevent(AllZEvents, NextPositions, Index)
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).
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index_of(A-Offset-Stride-Loop, A-NLoops-SubLoop, Index-A) :-
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nth0(SubLoop, Loop, LoopPosition-_),
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Index is Offset + NLoops*Stride + LoopPosition.
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next(A-_-_-Loop, A-NLoops-SubLoop, A-NextNLoops-NextSubLoop) :-
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length(Loop, LoopLen),
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( SubLoop < LoopLen - 1
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-> NextNLoops is NLoops, NextSubLoop is SubLoop + 1
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; NextNLoops is NLoops + 1, NextSubLoop is 0).
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% Everything above this is not needed to get the input answer
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% starts(Starts),
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% maplist([S, S-Off-Stride-Loop]>>(zloop([], S, 0, [], Off, Stride, Loop)),
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% Starts, Loops).
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% then find the LCD of the strides (which are equal to offsets).
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zloop(_, _, _, Zs, Offset, Stride, 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, Offset, Stride, Loop) :-
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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, Offset, Stride, Loop).
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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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same_elements([_]).
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same_elements([X-_, Y-Z2 | Cdr]) :- X =:= Y, same_elements([Y-Z2 | Cdr]).
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