拼合列表 [英] Flattening a list
问题描述
尝试通过 http://来解决练习07 www.ic.unicamp.br/~meidanis/courses/mc336/2009s2/prolog/problemas/
我从一个简单的迭代开始,如下所示:
I've started with a single iteration which looks like following
my_flatten1([], []).
my_flatten1([[A|T]|U], [A|V]) :-
append(T, U1, V),
my_flatten1(U, U1).
my_flatten1([A|T], [A|U]) :-
not(is_list(A)),
my_flatten1(T, U).
is_flat(A) :-
my_flatten1(A, A).
对于以下一组查询似乎效果很好
it seems to work just fine for the following set of queries
my_flatten1([a, [b, [c, d], e]], X).
my_flatten1(X, [a, b, c]).
my_flatten1(X, [a|T]).
my_flatten1(X, [a, b, A]).
my_flatten1([a, X], M).
my_flatten1([a|X], M).
is_flat([a|X]).
is_flat([a,[c]|X]).
is_flat([F,[c]|X]).
my_flatten1(A, B).
my_flatten1([A], B).
my_flatten1([[A]], B).
my_flatten1([[a|A]], B).
my_flatten1([a|A], B).
my_flatten1([X|B], [1,2,3,4]).
my_flatten1([[a,c|D]|X], [a|B]).
但是我没有成功地基于my_flatten1
构建my_flatten
.总是有一些查询失败或以无休止的循环结束,或者仅产生一个最明显的结果.
However I wasn't successful to build my_flatten
based on my_flatten1
. There's always some queries that fail or end up in endless loops, or produce just one, most obvious result.
编辑以明确说明我要做什么,例如,我可以使用变量作为第一个参数调用my_flatten1
以便分发括号:
Edit to clarify what I am after, for example I can call my_flatten1
with a variable as a first argument in order to distribute brackets:
?- my_flatten1(X, [a, b]).
X = [[a], [b]] ;
X = [[a], b] ;
X = [[a, b]] ;
X = [a, [b]] ;
X = [a, b].
推荐答案
我不确定您单击问题标题时是否知道99个Prolog问题包含解决方案?
I'm not sure if you are aware that the 99 Prolog problems contain solutions when you click on the problem title?
无论如何,my_flatten
的外观例如如下:
Anyways, my_flatten
looks, for example, like following:
my_flatten(X,[X]) :- \+ is_list(X).
my_flatten([],[]).
my_flatten([H|T],R) :-
my_flatten(H,HFlat),
my_flatten(T,TFlat),
append(HFlat,TFlat,R).
一些查询:
?- my_flatten([[]],R).
R = [].
?- my_flatten([[1],[2]],R).
R = [1, 2].
?- my_flatten([[1],[[3]]],R).
R = [1, 3].
编辑
@ lambda.xy.y正确观察到,以上版本的查询不会终止:
As correctly observed by @lambda.xy.y, above version does not terminate for the query:
?- my_flatten(X,[X]).
所以我看了SWI内置的flatten/2
的行为并观察到:
So I took a look at the behaviour of SWI's built-in flatten/2
and observed:
?- flatten([],[]).
true.
?- flatten([],X).
X = [].
?- flatten(X,[]).
false.
?- flatten(X,Y).
Y = [X].
?- flatten(X,[X]).
true.
实施:
my_flatten(L,R) :-
my_flatten(L,[],Flat),
!,
R=Flat.
my_flatten(X,R,[X|R]) :- \+ is_list(X), !.
my_flatten([],R,R) :- !.
my_flatten([H|T],A1,R) :- !,
my_flatten(H,A2,R),
my_flatten(T,A1,A2).
my_flatten(NonList,T,[NonList|T]).
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