如何从 Prolog 中的数组中删除特定外观的元素？

发布于 2024-10-01 00:40:36 字数 165 浏览 3 评论 0原文

我想仅删除给定数组中每个元素的第二次出现并将结果返回到新数组中。给定的数组可以包含原子元素，但也可以包含类似列表的元素。
谓词应该这样调用：delete_second(L1,L2).
L1=[1,2,4,1,[1,2,3,[4]],2,1]
L2=[1,2,4,[1,3,[]],2,1]。

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溺孤伤于心 2024-10-08 00:40:36

您可以使用两个累加器列表。在一个累加器中，您将拥有仅出现一次的项目，而在另一个累加器上，您将拥有出现多次的项目。
因此，您必须遍历输入列表的所有项目，更新这些累加器，并根据需要从输出列表中选择和丢弃该项目。

像这样的东西：

delete_second(In, Out):-
delete_second(In, [], [], _, _, Out).

delete_second([], Once, Twice, Once, Twice, []):- !.
delete_second([X|Tail], Once, Twice, NOnce, NTwice, [Y|Out]):-
  delete_second(X, Once, Twice, MOnce, MTwice, Y),
  !,
  delete_second(Tail, MOnce, MTwice, NOnce, NTwice, Out).
delete_second([X|Tail], Once, Twice, NOnce, NTwice, [X|Out]):-
  member(X, Twice),
  !,
  delete_second(Tail, Once, Twice, NOnce, NTwice, Out).
delete_second([X|Tail], Once, Twice, NOnce, NTwice, Out):-
  append(OnceP, [X|OnceT], Once),
  append(OnceP, OnceT, MOnce),
  !,
  delete_second(Tail, MOnce, [X|Twice], NOnce, NTwice, Out).
delete_second([X|Tail], Once, Twice, NOnce, NTwice, [X|Out]):-
  !,
  delete_second(Tail, [X|Once], Twice, NOnce, NTwice, Out).

You might use two accumulator lists. In one accumulator you would have the items that appeared just once, and on the other accumulator you would have the items that appeared more than once.
So you would have to go through all the items of the input list updating those accumulators and selecting and discarding the item from the output list if required.

Something like:

delete_second(In, Out):-
delete_second(In, [], [], _, _, Out).

delete_second([], Once, Twice, Once, Twice, []):- !.
delete_second([X|Tail], Once, Twice, NOnce, NTwice, [Y|Out]):-
  delete_second(X, Once, Twice, MOnce, MTwice, Y),
  !,
  delete_second(Tail, MOnce, MTwice, NOnce, NTwice, Out).
delete_second([X|Tail], Once, Twice, NOnce, NTwice, [X|Out]):-
  member(X, Twice),
  !,
  delete_second(Tail, Once, Twice, NOnce, NTwice, Out).
delete_second([X|Tail], Once, Twice, NOnce, NTwice, Out):-
  append(OnceP, [X|OnceT], Once),
  append(OnceP, OnceT, MOnce),
  !,
  delete_second(Tail, MOnce, [X|Twice], NOnce, NTwice, Out).
delete_second([X|Tail], Once, Twice, NOnce, NTwice, [X|Out]):-
  !,
  delete_second(Tail, [X|Once], Twice, NOnce, NTwice, Out).

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