[英]C++ library method for intersection of two unordered_set
I have two unordered_set and want the intersection of those. 我有两个unordered_set并想要它们的交集。 I can't find a library function to do that.
我找不到一个库函数来做到这一点。
Essentially, what I want is this: 基本上,我想要的是这样的:
unordered_set<int> a = {1, 2, 3};
unordered_set<int> b = {2, 4, 1};
unordered_set<int> c = a.intersect(b); // Should be {1, 2}
I can do something like 我可以做点什么
unordered_set<int> c;
for (int element : a) {
if (b.count(element) > 0) {
c.insert(element);
}
}
but I think there should be a more convenient way to do that? 但我认为应该有更方便的方法吗? If there's not, can someone explain why?
如果没有,有人可以解释原因吗? I know there is set_intersection, but that seems to operate on vectors only?
我知道有set_intersection,但这似乎仅适用于矢量?
Thanks 谢谢
In fact, a loop-based solutions is the best thing you can use with std::unordered_set
. 事实上,基于循环的解决方案是您可以使用
std::unordered_set
的最佳选择。
There is an algorithm called std::set_intersection
which allows to find an intersection of two sorted ranges: 有一个名为
std::set_intersection
的算法,它允许查找两个有序范围的交集:
Constructs a sorted range beginning at d_first consisting of elements that are found in both sorted ranges [first1, last1) and [first2, last2).
构造一个从d_first开始的排序范围,该排序范围由在排序范围 [first1,last1]和[first2,last2)中找到的元素组成。
As you deal with std::unordered_set
, you cannot apply this algorithm because there is no guaranteed order for the elements in std::unordered_set
. 在处理
std::unordered_set
,您无法应用此算法,因为std::unordered_set
的元素没有保证顺序。
My advice is to stick with loops as it explicitly says what you want to achieve and has a linear complexity ( O(N) , where N is a number of elements in the unordered set you traverse with a for loop ) which is the best compexity you might achieve. 我的建议是坚持使用循环,因为它明确地说明了你想要实现的东西,并且具有线性复杂度( O(N) ,其中N是你用for循环遍历的无序集合中的元素数量),这是最好的复杂性你可能会实现。
There is a function from std
called set_intersection
. std
有一个名为set_intersection
的函数。 However, it would have a very high complexity using it with std::set
as input parameter.. A better solution is, create two vectors from those sets and use set_intersection
with vectors as input parameters. 但是,使用
std::set
作为输入参数会有很高的复杂性。更好的解决方案是,从这些集合中创建两个向量,并使用带向量的set_intersection
作为输入参数。
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