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marginally more readable d8p2

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Dory 2023-12-10 11:30:50 -08:00
parent 668be81650
commit 16733a03c8
1 changed files with 24 additions and 27 deletions
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51
08/part2.pl
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@ -10,15 +10,16 @@ answer(Answer) :-
% unify2 combines 2 routes into one with its own stride-offsets-dests
unify2(Route1, Route2, NewRoute) :-
writef('Combining %t + %t', [Route1, Route2]),
once(findnsols(2, S, converge(Route1, Route2, S), SolutionPair)),
SolutionPair = [NewA-LenA-NewZ, _-LenB-_],
NewStride is LenB - LenA,
NewRoute = NewA-(NewStride-LenA-[0-NewZ]).
NewRoute = NewA-(NewStride-LenA-[0-NewZ]),
writef(' --> %t\n', [NewRoute]).
% Len = Stride1*X1 + Offset1 + Dest1 = Stride2*X2 + Offset2 + Dest2
% For performance, Route1's Stride should =< Route2's Stride
converge(Route1, Route2, NewA-Len-NewZ) :-
writef('Combining %t - %t\n', [Route1, Route2]),
Route1 = A1-(Stride1-Offset1-Dests1),
Route2 = A2-(Stride2-Offset2-Dests2),
natnum(X2),
@ -28,42 +29,38 @@ converge(Route1, Route2, NewA-Len-NewZ) :-
atom_concat(A1, A2, NewA), atom_concat(Z1, Z2, NewZ).
routes(Starts, Routes) :-
maplist([S, S-Route]>>(zloop(S, Route)), Starts, Routes).
maplist([S, S-Route]>>(route_at(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),
% route_at(N, Node, Dests, AllDests) means going N steps will arrive at Node
% passing through Dests.
route_at(Start, Route) :- route_at(0, Start, [], Route).
route_at(N, FirstZ, [FirstZN-FirstZ | Zs], Stride-Offset-AllZs) :-
Stride is N - FirstZN, direction_looped(Stride),
Offset is FirstZN,
maplist({Offset}/[N-X, M-X]>>(M is N-Offset), [FirstZN-FirstZ | Zs], AllZs),
!.
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).
route_at(N, At, Dests, AllDests) :-
( is_end(At)
-> append(Dests, [N-At], NextDests)
; NextDests = Dests),
Nplus1 is N + 1, step_at(N, Step), call(Step, At, NextNode),
route_at(Nplus1, NextNode, NextDests, AllDests).
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]).
% Step is the N-th step (counting starts from 0).
step_at(N, Step) :-
direction_list(Dir), length(Dir, DirLen), Remainder is N mod DirLen,
nth0(Remainder, Dir, Step).
direction_list(Dir) :- direction(Str), atom_chars(Str, Dir).
direction_len(Len) :- direction_list(D), length(D, Len).
direction_looped(Len) :- direction_list(D), length(D, DLen), 0 is Len mod DLen.
% pick([[1,2,3], [4], [5,6]], X). X = [1,4,5]; X = [1,4,6]; X = [2,4,5]; ...
% pick one item from each sublist of ListOfLists & put them into Items in order.
% [[1,2,3], [4], [5,6]] -> [1,4,5]; [1,4,6]; [2,4,5]; [2,4,6]; [3,4,5]; [3,4,6].
pick(ListOfLists, Items) :-
maplist([SubList, X]>>(member(X, SubList)), ListOfLists, Items).