Question

我正在尝试编写一个程序，用于从Prolog中的列表中删除最后一个元素。除了member / 2之外，我不应该在这里使用内置谓词。我知道我必须为此使用递归。但我对此并不是很好。我得到了这个，但它失败了：

% remove_last/3 with (Element, List, Resultlist)
remove_last(X,[X|T],NT):-
   remove_last(X,T,NT).

我认为Prolog应该削减列表的头部，扫描尾部，重新执行直到尾部与Element匹配，删除它并恢复剩余列表。但我不知道如何将其放入代码中。我会很感激任何提示！

Answer 1

这是一个更易读的答案：

remove_last(X, [X|L], L) :-
    maplist(dif(X), L).
remove_last(X, [H|T], [H|L]) :-
    remove_last(X, T, L).

显然，它使用的内置插件显然是被禁止的，但我认为dif/2非常重要，它可能被认为是合法的，例如\+用于此类内容（maplist相同）。

表现得非常好：

?- remove_last(2,[1,2,3,2,5],Z).               % "Normal" use
Z = [1, 2, 3, 5] ;
false

?- remove_last(Z,[1,2,3,2,5],[1,2,3,5]).       % Searching X given the two lists
Z = 2 ;
false.

?- remove_last(2,X,[1,2,3,5]).                 % Searching the original list
X = [1, 2, 2, 3, 5] ;
X = [1, 2, 3, 2, 5] ;
X = [1, 2, 3, 5, 2] ;
false.

如果所有内容都是变量，那么它有效，但不能正确枚举答案：

?- remove_last(X,L,M).
L = [X],
M = [] ;
L = [X, _1124],
M = [_1124],
dif(X, _1124) ;
L = [X, _1302, _1308],
M = [_1302, _1308],
dif(X, _1308),
dif(X, _1302) ;
…

您可以使用length/2正确枚举答案：

?- length(L, _), remove_last(X,L,M).
L = [X],
M = [] ;
L = [X, _1230],
M = [_1230],
dif(X, _1230) ;
L = [_692, X],
M = [_692] ;
L = [X, _1408, _1414],
M = [_1408, _1414],
dif(X, _1414),
dif(X, _1408) ;
L = [_1242, X, _1254],
M = [_1242, _1254],
dif(X, _1254) ;
L = [_692, _698, X],
M = [_692, _698] ;

运行时间

在1000个随机数字的列表中：

?- time(remove_last(3,[8,1,5,1,8,2,0,1,8,2,0,4,2,1,6,8,6,1,0,3,5,6,3,5,3,1,8,7,7,4,8,8,0,9,3,8,7,9,0,6,4,8,1,9,2,9,0,1,0,0,9,7,7,5,2,5,8,5,1,6,8,3,2,8,7,2,9,0,5,9,5,0,9,6,7,1,4,9,7,1,3,5,0,0,0,3,3,7,7,7,9,4,9,8,0,8,7,0,7,7,0,8,3,0,9,3,4,8,8,1,3,7,8,8,8,2,7,4,2,8,4,0,6,9,3,9,0,2,0,7,9,5,9,0,8,3,3,4,3,4,2,3,0,4,6,8,9,3,6,0,9,7,6,4,8,7,3,8,9,5,4,2,7,2,9,3,0,5,3,7,9,0,3,4,5,3,5,0,9,4,4,5,2,9,0,9,2,6,1,6,3,4,6,3,9,9,0,6,0,7,9,3,8,3,0,7,1,3,5,4,9,1,9,0,4,8,2,5,3,7,5,7,2,7,3,2,1,7,9,3,9,3,6,4,3,6,9,8,1,3,7,6,0,8,0,4,6,6,4,4,8,5,1,8,5,9,1,7,6,2,8,0,2,5,0,7,2,7,9,2,6,7,6,2,8,2,1,9,2,5,6,8,0,2,2,2,3,2,0,6,9,5,7,3,8,9,9,6,9,9,3,3,7,5,9,0,2,2,6,3,7,1,4,7,4,0,9,1,1,5,2,2,3,4,7,8,8,3,4,1,2,6,8,2,8,0,0,7,5,6,5,9,0,6,5,6,4,0,4,5,6,7,4,5,1,5,9,9,9,3,6,1,0,6,8,6,0,6,6,0,9,4,2,3,8,8,8,4,3,0,4,7,1,4,7,7,4,6,6,3,0,0,7,1,5,1,6,2,9,1,3,5,0,6,6,4,8,7,0,6,3,7,0,0,8,6,9,3,1,2,6,2,6,1,0,1,7,4,6,4,3,9,2,5,5,7,4,1,8,8,1,3,8,0,9,0,9,7,5,5,9,6,6,3,8,3,1,5,9,5,1,0,6,7,1,5,0,4,7,1,1,4,4,9,5,8,4,2,1,5,3,2,4,6,8,6,8,6,9,5,5,7,3,6,0,6,0,3,8,0,0,5,1,8,7,3,9,9,3,2,6,7,4,2,6,5,4,2,6,8,6,2,2,3,5,0,5,2,8,5,4,0,0,3,5,0,8,2,0,1,7,3,0,2,4,3,8,4,9,5,2,5,9,1,3,4,3,3,6,7,7,3,6,0,8,8,4,1,3,9,0,1,3,3,4,0,8,4,2,5,1,0,5,2,5,2,3,1,2,3,9,3,5,2,8,7,9,3,4,0,0,7,5,1,7,5,8,2,6,4,8,4,7,0,5,9,7,3,4,8,9,6,4,1,8,6,8,5,0,0,8,9,2,5,8,0,0,6,8,1,9,3,7,2,6,3,3,4,0,4,1,6,3,7,5,2,5,8,9,8,1,7,1,5,2,8,7,5,8,3,7,4,9,6,2,3,7,1,0,2,9,9,3,3,2,9,6,0,3,4,0,4,4,4,5,1,3,2,6,7,5,7,9,4,4,4,1,9,7,4,0,5,2,6,1,2,4,4,7,3,8,9,2,8,0,3,1,5,0,7,7,8,1,9,6,1,9,4,9,7,6,4,0,2,1,7,9,0,8,9,9,6,6,3,7,8,7,1,1,7,3,3,4,4,8,0,2,1,1,7,2,6,8,6,2,1,2,2,4,7,5,9,3,4,4,9,3,0,8,4,4,4,5,8,0,2,5,5,0,6,2,1,7,4,0,7,1,6,4,3,9,0,1,1,0,9,3,0,7,1,2,8,4,0,2,7,2,8,6,5,1,8,0,0,4,5,6,0,1,9,6,1,5,1,9,0,0,2,7,1,2,4,1,2,0,8,9,1,4,7,3,1,1,8,8,4,4,5,8,0,0,5,0,9,7,1,1,5,1,6,4,0,4,8,7,0,2,7,9,1,4,6,2,8,9,1,6,1,4,0,7,9,9,9,0,6,8,8,2,0,4,4,6,0,0,2,0,0,6,4,6,2,5,5,7,7,8,1,9,6,6,6,7,8,5,7,0,1,0,9,1,4,2,1,7,2,1,6,7,6,4,7,5,7,7,7,4,4,2,6,7,1,1,3,3,7,6,2,9,8,9,9,2,4,7,2,2,8,8,3,3,6,4,2,4,4,5,4,0,8,3,4,6,5,3,1,1,0,3,0],Z)).
% 10,996 inferences, 0.000 CPU in 0.002 seconds (0% CPU, Infinite Lips)
Z = [8, 1, 5, 1, 8, 2, 0, 1, 8|...] .

从prolog中的列表中删除元素的最后一次出现？

1 个答案:

运行时间