Prolog:将列表拆分为两个列表(唯一项/重复项) [英] Prolog: splitting a list into two lists (unique items / duplicate items)

问题描述

我一直在尝试将给定列表拆分为两个不同的列表:唯一列表和重复列表.例如，如果我们有列表 [1, 1, 2, 3, 3, 4, 5] 我希望唯一列表是 [2, 4, 5] 并复制为 [1, 3].我不希望列表中的所有 1 都在重复列表中.我只需要其中之一.我现在的代码:

I have been trying to split a given list into two different lists: Unique and Duplicate. For example, if we have the list [1, 1, 2, 3, 3, 4, 5] I want the Unique list to be [2, 4, 5] and Duplicate to be [1, 3]. I don't want all the 1's in the list to be in the Duplicate list. I just need one of it. The code I have right now:

compareL([_|[]], Unique, Dup).    
compareL([X3,Y3 | Tail], [X3 | Unique], Dup) :-
    X3 == Y3,
    compareL([Y3 | Tail], Unique, Dup). 
compareL([X3,Y3 | Tail], Unique, [X3 | Dup]) :- 
    X3 = Y3,
    skipDups(X3, Tail, Unique, Dup).

skipDups(_, [], Unique, Dup).   
skipDups(X3,[Y3 | Tail], Unique, Dup) :- 
    X3 == Y3,
    compareL([Y3 | Tail], Unique, Dup).
skipDups(X3,[Y3 | Tail], Unique, Dup) :-
    X3 = Y3,
    skipDups(X3, Tail, Unique, Dup).

如果我运行 compareL([1, 1, 2, 3, 3, 4, 5], Unique, Dup)，使用上面给出的示例列表. 我得到:

Using the example list given above if I run compareL([1, 1, 2, 3, 3, 4, 5], Unique, Dup). I get:

Unique = [2, 4|_G1954],
Dup = [1, 3|_G1948].

我无法弄清楚为什么在两个列表的末尾我都会得到_G1954"和_G1948".任何帮助，将不胜感激.谢谢.

I can't figure out why towards the end of both lists I am getting '_G1954' and '_G1948'. Any help would be appreciated. Thanks.

推荐答案

这里有一个解决方案，关键是 take/4 消耗所有匹配的前导项，从而可以轻松测试列表( [_|_] 匹配任何包含至少 1 个元素的列表)

here is a solution, the key is take/4 that consumes all matching leading items, thus enabling easy testing of the list ( [_|_] matches any list of at least 1 element )

compareL([], [], []).
compareL([X|Xs], U, D) :-
    (   take(X, Xs, [_|_], Ys)
    ->  compareL(Ys, U, B), D = [X|B]
    ;   compareL(Xs, A, D), U = [X|A]
    ).

take(X, [X|Xs], [X|R], Ys) :-
    !, take(X, Xs, R, Ys).
take(_, Ys, [], Ys).

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