113 lines
4.4 KiB
Perl
113 lines
4.4 KiB
Perl
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:- use_module(library(pio)).
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:- use_module(library(dcg/basics)).
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:- op(700, xfx, [supports, is_way_above]).
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:- initialization(main, main).
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main([FileName|_]) :-
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input(FileName, Bricks),
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stack(Bricks, StackedBricks),
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support_listing(StackedBricks, Supporters, SupportMap),
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length(Bricks, Len), TopBrick is Len - 1,
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findall(
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Goners,
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( between(0, TopBrick, Brick),
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remove(SupportMap, [Brick], Supporters, Goners)),
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GonerCounts),
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sum_list(GonerCounts, Answer),
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write(Answer), nl.
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remove(_, [], _, -1).
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remove(SupportMap, [N|ToKills], Supporters, Goners) :-
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SupportedByN = SupportMap.N,
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foldl(decrement_supporter_count, SupportedByN, Supporters, NewSupporters),
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convlist({NewSupporters}/[X, X]>>(is_goner(NewSupporters, X)),
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SupportedByN, ToKillMore),
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append(ToKills, ToKillMore, ToKillNext),
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remove(SupportMap, ToKillNext, NewSupporters, NextGoners),
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Goners is NextGoners + 1.
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is_goner(Supporters, M) :- Supporters.M =< 0.
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decrement_supporter_count(M, Supporters, NewSupporters) :-
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NewCount is Supporters.M - 1,
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NewSupporters = Supporters.put(M, NewCount).
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% StackedBricks is sorted by decreasing top edge
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support_listing(StackedBricks, SupportedCount, SupportingMap) :-
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findall(
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N=SupportedListLen,
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( append(_, [Brick1|Belows], StackedBricks),
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supported_by(Brick1, Belows, SupportedList),
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length(SupportedList, SupportedListLen),
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Brick1 = N-_-_-_),
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SupportedLists),
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SupportedCount = brick{}.put(SupportedLists),
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sort(2, @=<, StackedBricks, StackSortedByBottoms),
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findall(
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M=SupportingList,
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( append(_, [Brick2|Aboves], StackSortedByBottoms),
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supporting(Brick2, Aboves, SupportingList),
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Brick2 = M-_-_-_),
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SupportingLists),
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SupportingMap = brick{}.put(SupportingLists).
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% Aboves need to be sorted by increasing bot edge
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supporting(_Brick, [], []).
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supporting(Brick, [Above|_], []) :- Above is_way_above Brick, !.
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supporting(Brick, [Above|Aboves], Supportings) :-
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supporting(Brick, Aboves, NextSupportings),
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( Brick supports Above
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-> Above = N-_-_-_, Supportings = [N|NextSupportings]
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; Supportings = NextSupportings).
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% Belows need to be sorted decreasing by top edge
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supported_by(_Brick, [], []).
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supported_by(Brick, [Below|_], []) :- Brick is_way_above Below, !.
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supported_by(Brick, [Below|Belows], SupportedBy) :-
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supported_by(Brick, Belows, NextSupportedBy),
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( Below supports Brick
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-> Below = N-_-_-_, SupportedBy = [N|NextSupportedBy]
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; SupportedBy = NextSupportedBy).
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is_way_above(_-_-_-(Z2bot-_), _-_-_-(_-Z1top)) :- Z2bot > Z1top + 1.
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supports(Brick1, Brick2) :-
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overlap(Brick1, Brick2),
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Brick1 = _-_-_-(_-Z1top), Brick2 = _-_-_-(Z2bot-_), Z2bot =:= Z1top + 1.
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stack(Bricks, StackedBricks) :-
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empty_heap(H0), foldl(stack1, Bricks, H0, Heap),
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heap_to_list(Heap, HeapList),
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maplist([_-Brick, Brick]>>(true), HeapList, StackedBricks).
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stack1(Brick, Heap, NewHeap) :-
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( max_of_heap(Heap, OldZtop, OldTop), overlap(Brick, OldTop)
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; empty_heap(Heap), OldZtop is 0),
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Brick = N-X-Y-(Zbot-Ztop),
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NewZbot is OldZtop + 1, NewZtop is NewZbot + (Ztop - Zbot),
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add_to_maxheap(Heap, NewZtop, N-X-Y-(NewZbot-NewZtop), NewHeap),
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!.
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stack1(Brick, Heap, NewHeap) :-
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get_from_maxheap(Heap, LastZtop, LastTopBrick, HeapWithoutTop),
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stack1(Brick, HeapWithoutTop, NewHeapWithoutTop),
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add_to_maxheap(NewHeapWithoutTop, LastZtop, LastTopBrick, NewHeap).
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overlap(_-(Xa1-Xa2)-(Ya1-Ya2)-_, _-(Xb1-Xb2)-(Yb1-Yb2)-_) :-
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Xa1 =< Xb2, Xa2 >= Xb1, Ya1 =< Yb2, Ya2 >= Yb1.
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% input parsing stuff below. Brick indexing is for debugging.
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input(FileName, SortedBricks) :-
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phrase_from_file(bricks(0, Bricks), FileName),
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sort(2, @=<, Bricks, SortedBricks).
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bricks(_, []) --> eos, !.
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bricks(N, [Line|Lines]) --> {Next is N+1}, brick(N, Line), bricks(Next, Lines).
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brick(N, N-(X1-X2)-(Y1-Y2)-(Z1-Z2)) -->
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number(X1), ",", number(Y1), ",", number(Z1), "~",
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number(X2), ",", number(Y2), ",", number(Z2), "\n".
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% maxheap wrapper. PriX = -Pri, which is the Ztop
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max_of_heap(H, Pri, Key) :- min_of_heap(H, PriX, Key), Pri is -PriX.
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add_to_maxheap(H0, Pri, Key, H) :- PriX is -Pri, add_to_heap(H0, PriX, Key, H).
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get_from_maxheap(H0, Pri, Key, H) :- get_from_heap(H0, PriX, Key, H), Pri is -PriX.
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% Can probably do 2 maps, one by top edges and one by bottom edges and lookup
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