如何找到两个std：set在C ++中？ [英] how to find the intersection of two std:set in C++?

问题描述

我一直在尝试找到两个std :: set在C ++中的交集，但我一直收到一个错误。

I have been trying to find the intersection between two std::set in C++, but I keep getting an error.

我创建了一个小样本测试

I created a small sample test for this

#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
using namespace std;

int main() {
  set<int> s1;
  set<int> s2;

  s1.insert(1);
  s1.insert(2);
  s1.insert(3);
  s1.insert(4);

  s2.insert(1);
  s2.insert(6);
  s2.insert(3);
  s2.insert(0);

  set_intersection(s1.begin(),s1.end(),s2.begin(),s2.end());
  return 0;
}

后一个程序不会生成任何输出，使用以下值设置（我们称为s3）：

The latter program does not generate any output, but I expect to have a new set (let's call it s3) with the following values:

s3 = [1,3]

而我得到的错误：

test.cpp： （std :: _ Rb_tree_const_iterator< int>，std :: _ Rb_tree_const_iterator< int>，std :: _ Rb_tree_const_iterator< int>，std（）'：
test.cpp：19：error：没有匹配的函数:: _ Rb_tree_const_iterator< int>）'

我理解这个错误，是 set_intersection ，它接受 Rb_tree_const_iterator< int> 作为参数。

What I understand out of this error, is that there's no definition in set_intersection that accepts Rb_tree_const_iterator<int> as parameter.

此外，我假设std :: set.begin（）方法返回此类型的对象，

Furthermore, I suppose the std::set.begin() method returns an object of such type,

有没有更好的方法来找到两个std :: set在C ++的交集？最好是内置函数？

is there a better way to find the intersection of two std::set in C++? Preferably a built-in function?

非常感谢！

推荐答案

set_intersection

template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_intersection ( InputIterator1 first1, InputIterator1 last1,
                                InputIterator2 first2, InputIterator2 last2,
                                OutputIterator result );

通过执行以下操作来修复此问题：

Fix this by doing something like

...;
set<int> intersect;
set_intersection(s1.begin(),s1.end(),s2.begin(),s2.end(),
                  std::inserter(intersect,intersect.begin()));

您需要一个 std :: insert 迭代器因为该集现在是空的。我们不能使用back_或front_inserter，因为set不支持这些操作。

You need a std::insert iterator since the set is as of now empty. We cannot use back_ or front_inserter since set doesnt support those operations.

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