list - 从列表序言中删除相邻的重复项

Question

我是 Prolog 的新手，我需要从列表中删除重复项，如下例所示。

?- remove([a,a,b,c,a,a,b,c,b,a,a],X).
X = [a,b,c,a,b,c,b,a]

Answer 1

如果我理解正确，您需要删除相邻的重复项。只需复制跳过第一个相邻元素的元素。我会让你完成代码...

remove([X,X|Rest], [X|Rest1]) :-
   !,   % this commit avoid the logical alternative you'll code below
   .... % recurse to get Rest1 from Rest
remove([X|Rest], [X|Rest1]) :-
   % recurse to get Rest1 from Rest
% remember the base case !!

编辑错误指出，这种天真的 remove/2 是错误的。我已经更正了添加 remove/3 谓词，该谓词对见证进行了复制，即元素前瞻。

remove([X|Xs], [X|Ys]) :-
  remove(X, Xs, Ys).
remove(X, [X|Xs], Ys) :-
  !,  % discard the duplicate
  ... % recurse to get Ys from Xs, with same witness
remove(_, [X|Xs], [X|Ys]) :-
  ... % the cut above ensure that here we must change witness when recursing
% as always, remember the base case !!