Set in STL, intersection and difference sets

Set's keys are automatically sorted, corresponding to the convergence of the set difference can be used to this ordered characteristics, time complexity is O (m+n), m,n respectively two container size

1.set_union can be used to find the set of two sets, which is a stable operation because the relative position between elements does not change.

The source code is as follows:

Template <class inputiterator1,class inputiterator2,class outputiterator> outputiterator set_union
( InputIterator1 First1,inputiterator1 last1,
						 InputIterator2 first2,inputiterator2 last2,
						 outputiterator Result)
{while
	(First1!=last1&&first2!=last2)
	{
	if (*first1<*first2)
	{
		* Result=*first1;
		++first1;
	}
	else if (*first1>*first2)
	{
		*result=*first2;
		++first2;
	}
	else     //equal situation
	{
		*result=*first1;
		++first1;
		++first2;
	}
	++result;
	}
	return copy (First2,last2,copy (First1,last1,result));

2.set_intersection can be used to find the intersection of two sets

The source code is as follows:

Template <class inputiterator1,class inputiterator2,class outputiterator >
outputiterator set_intersection (InputIterator1 first1,inputiterator1 Last1,
	                          InputIterator2 First2,inputiterator2 last2,
							  outputiterator result)
{while
	(first1!=last1&& First2!=last2)
	{
		if (*first1<*first2)
		{
			++first1;
		}
		else if (*first1>*first2)
		{
			++first2
		}
		else 
		{      //*first1==*first2, this element is an element of intersection
			*result=*first1;
			++first1;
			++first2;
			++result
		}
	}
	return result;
}

3.set_diference is used to find the difference set of two sets

The source code is as follows:

Template <class inputiterator1,class inputiterator2,class outputiterator> outputiterator set_difference
( InputIterator1 First1,inputiterator1 last1,
							  InputIterator2 first2,inputiterator2 last2,
							  outputiterator Result)
{while
	(First1!=last1&&first2!=last2)
	{
		if (*first1<*first2)    //*first1 <*first2, this element is the element of the difference set
		{
			*result=*first1;
			++first1;
			++result;
		}
		else if (*first1>*first2)
			++first2;
		else
		{
			++first1;
			++first2
		}
	}
	return copy (First1,last1,result);
}

Simple test:

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

int main ()
{
	set<int> s1,s2;
	S1.insert (1);
	S1.insert (2);
	S1.insert (3);
	S2.insert (2);
	S2.insert (3);
	S2.insert (4);
	Set<int>::iterator Iter1=s1.begin ();
	Set<int>::iterator iter2=s1.end ();
	Set<int>::iterator Iter3=s2.begin ();
	Set<int>::iterator iter4=s2.end ();
	vector<int> Res (10,0);
	Vector<int>::iterator iter;
	Iter=set_union (Iter1,iter2,iter3,iter4,res.begin ()); and set
	//iter=set_intersection (Iter1,iter2,iter3,iter4,res.begin ());//Intersection
	//iter=set_difference (Iter1, Iter2,iter3,iter4,res.begin ());  Difference set
	res.resize (Iter-res.begin ());  
	For (Iter=res.begin (); Iter!=res.end (); ++iter)
	{
	cout<<*iter<<endl;
	}
	System ("pause");
	return 0;
}