Prolog 可能删除列表中的元素 [英] Prolog possible removal of elements in a list

问题描述

我被要求尝试搜索所有可能的结果，从列表中的任何单个元素中删除任何数字.

I have been asked to try to search for all possible outcomes of, removing any numbers from any single elements from a list.

例如，如果我有一个列表 X = [1,2,3]

For example, if I have a list X = [1,2,3]

remove(X, Y)

我的结果是:

Y = [2,3]
Y = [1,1,3]
Y = [1,3]
Y = [1,2,2]
Y = [1,2,1]
Y = [1,2]

为此，我已经编写了 2 个解决方案，但我真的不知道我的解决方案有什么缺点.我的教授一直告诉我有更好的方法来做到这一点.

For this, I have already written 2 solutions, but I don't really know what is the cons of my solutions. My professor keeps telling me that there is a better way of doing this.

我的第一种方法:

test(S1, S2):-
    length(S1, L),
    M is L -1,
    between(0, M, N),
    remove(S1, S2, N).
remove([H|T], [H2|T2], Heap):-
    (
        Heap>0->
        H2 = H,
        remove(T, T2, Heap-1);
        between(1, H, N),
        H2 is H - N,
        T2 = T
    ).

我的第二种方法:

remove1([H|T], [H|TY]):-
    not(T=[]),
    remove1(T, TY).
remove1([H|T], S2):-
    between(1, H, X),
    HY is H - X,
    (   HY = 0-> S2 = T; S2=[HY|T]).

这两种方法都给出了相同的结果，但我真的很想知道如何才能做得更好.有人介意给我一些建议吗?

Both of the approaches are giving the same result, but I do really want to know how I can do it better. Would anyone mind giving me some advice please?

推荐答案

你必须:

• 从列表中选择一项(数字)
• 用小于所选项目的数字替换所选项目
• 或者完全删除所选项目

例如:

remove([N|Tail], [NX|Tail]):-
  succ(N1, N),
  between(1, N1, NX).
remove([_|Tail], Tail).
remove([N|Tail], [N|NTail]):-
  remove(Tail, NTail).

第一个子句选择列表中的第一项，并将该项替换为小于该项的数字.

The first clause selects the first item in the list, and replaces that item with a number which is less than the item.

第二个子句从列表中删除该项目(如您的示例所示，当您将 N 减去所选项目 (N) 时，它不会出现在第二个列表中.

The second clause removes the item from the list (as shown in your examples when you subtract N to the selected item (N) it does not appear in the second list.

第三个子句应用递归，将头项保持原样并将过程应用于其余列表.

The third clause applies recursion, leaving the head item as-is and applies the procedure to the remaining list.

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