d8p2 final optimized general solution

2023-12-09 16:41:07 -08:00
parent a997d00c89
commit cd18e701c5
3 changed files with 116 additions and 37 deletions
--- a/08/part2.unoptimized.pl
+++ b/08/part2.unoptimized.pl
@@ -0,0 +1,83 @@
+:- 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).