aoc23/08/part2.unoptimized.pl

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2023-12-09 18:41:07 -06:00
:- op(700, xfx, l).
:- op(700, xfx, r).
From l To :- From to To-_.
From r To :- From to _-To.
answer(Answer) :-
starts(Starts),
routes(Starts, Routes),
collapse_routes(Routes, _-(_-Answer-_)).
collapse_routes([X], X).
collapse_routes(Routes, Collapsed) :-
writef('Collapsing: %t\n', [Routes]),
sort(2, @=<, Routes, [Route1, Route2 | CdrRoutes]),
unify2(Route1, Route2, NewRoute),
collapse_routes([NewRoute | CdrRoutes], Collapsed).
% unify2 combines 2 routes into one with its own stride-offsets-dests
unify2(Route1, Route2, Route12) :- unify2(Route1, Route2, 0-0-0-0, [], Route12).
unify2(Route1, Route2, N1-Dest1-N2-Dest2, Founds, NewRoute) :-
Route1 = A1-(Stride1-Offset1-Dests1),
Route2 = A2-(Stride2-Offset2-Dests2),
nth0(Dest1, Dests1, C1-Z1),
nth0(Dest2, Dests2, C2-Z2),
Len1 is Offset1 + Stride1*N1 + C1,
Len2 is Offset2 + Stride2*N2 + C2,
next(Dests1, N1-Dest1, NextN1-NextDest1),
( Len1 =:= Len2
-> ( Founds = [OldLen]
-> atom_concat(A1, A2, NewA), atom_concat(Z1, Z2, NewZ),
NewStride is Len1 - OldLen,
NewRoute = NewA-(NewStride-OldLen-[0-NewZ]),
!
; unify2(Route1, Route2, NextN1-NextDest1-N2-Dest2, [Len1], NewRoute)
)
; Len1 < Len2
-> unify2(Route1, Route2, NextN1-NextDest1-N2-Dest2, Founds, NewRoute)
; next(Dests2, N2-Dest2, NextN2-NextDest2),
unify2(Route1, Route2, N1-Dest1-NextN2-NextDest2, Founds, NewRoute)
).
% next(Dests, NumberOfLoops-WhichInternalZ, NextNumberOfLoops-NextInternalZ)
next(Dests, NLoops-Dest, NextNLoops-NextDest) :-
length(Dests, DestsLen),
( Dest < DestsLen - 1
-> NextNLoops is NLoops, NextDest is Dest + 1
; NextNLoops is NLoops + 1, NextDest is 0).
routes(Starts, Routes) :-
maplist([S, S-Route]>>(zloop(S, Route)), Starts, Routes).
% zloop builds a route (Stride-Offset-Internals for a particular starting node.
zloop(Node, Route) :- zloop([], Node, 0, [], Route).
zloop(_Direction, _Node, _Index, Zs, Stride-Offset-Dests) :-
Zs = [FirstZIndex-Z | _], reverse(Zs, [LastZIndex-Z | ReversedZs]),
DeltaZ is LastZIndex - FirstZIndex, DeltaZ =\= 0,
direction_len(Len),
divmod(DeltaZ, Len, _, 0),
Offset = FirstZIndex, Stride = DeltaZ,
foldl([Idx-Z, NewIdx-Z, Off, Off]>>(NewIdx is Idx - Off),
ReversedZs, ReversedDests, Offset, _),
reverse(ReversedDests, Dests),
!.
zloop(Directions, Node, Index, Zs, Route) :-
( is_end(Node)
-> append(Zs, [Index-Node], NewZs)
; NewZs = Zs
),
next_step(Directions, Move, Remain),
G =.. [Move, Node, To], G,
NewIndex is Index + 1,
zloop(Remain, To, NewIndex, NewZs, Route).
starts(Starts) :- findall(X, X to _, Nodes), include(is_start, Nodes, Starts).
is_start(Node) :- atom_chars(Node, [_, _, a]).
is_end(Node) :- atom_chars(Node, [_, _, z]).
next_step([Move | Remain], Move, Remain).
next_step([], Move, Remain) :- direction_list([Move | Remain]).
direction_list(Dir) :- direction(Str), atom_chars(Str, Dir).
direction_len(Len) :- direction_list(D), length(D, Len).