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问题描述
我一直在尝试在Prolog中创建谓词，以将整数列表分为正整数列表和负整数列表.
I've been trying to create a predicate in Prolog which splits a list of integers into a list of positive integers and into a list of negative integers.
示例查询具有预期结果:
Sample query with expected result:
?- split([1,-2,3,4,-8],X,Y).
X = [1,3,4],
Y = [-2,-8].
这是我到目前为止得到的代码:
This is the code I got so far:
split([], [], []).
split([Head|Tail], List1, List2) :- split(Tail, [Head|List1], List2), Head>=0.
split([Head|Tail], List1, List2) :- split(Tail, List1, [Head|List2]), Head<0.
我似乎无法弄清楚我在做错什么.
I can't seem to figure out what I'm doing wrong.
推荐答案
递归部分不太正确.
split([], [], []).
split([Head|Tail], [Head|List1], List2) :- Head>=0, split(Tail, List1, List2).
split([Head|Tail], List1, [Head|List2]) :- Head<0, split(Tail, List1, List2).
如果Head >= 0，应将Head添加到肯定列表中，而当Head < 0时，应添加到否定列表中.
The Head should be added to the positive list if Head >= 0 and to the negative list when Head < 0.
此外，最好在开头检查Head 的符号，因为这样可以防止不必要的递归调用.
Moreover, checking the sign of Head at the beginning is better, because it will prevent unnecessary recursive calls.
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