交集：
void Intersect(const vector<int>& A,const vector<int>& B,vector<int>& ans)
{
map<int, int> Counter;
const int ASize = A.size(),BSize = B.size();
for(int i=0; i<ASize; ++i)
Counter[A[i]] = 1;
for(int i=0; i<BSize; ++i)
{
if(Counter.count(B[i]))
Counter[B[i]] = 2;
}
map<int, int>::iterator it;
for(it=Counter.begin(); it!=Counter.end(); ++it)
{
if(it->second == 2)
ans.push_back(it->first);
}
}
并集：
void Union(const vector<int>& A,const vector<int>& B,vector<int>& ans)
{
set<int> Exist;
Exist.insert(A.begin(), A.end());
Exist.insert(B.begin(), B.end());
set<int>::iterator it;
for(it=Exist.begin(); it!=Exist.end(); ++it)
ans.push_back(*it);
}
差集：
void Difference(const vector<int>& A,const vector<int>& B,vector<int>& ans)
{
set<int> Unique;
Unique.insert(A.begin(), A.end());
const int BSize = B.size();
for(int i=0; i<BSize; ++i)
Unique.erase(B[i]);//删除在B中也存在的元素
set<int>::iterator it;
for(it=Unique.begin(); it!=Unique.end(); ++it)
ans.push_back(*it);
}
简单测试代码：
int a[] = {1,2,3,4,5,5,4,3,2,1,6,8,10,9,7};
int b[] = {2,2,4,4,8,8,6,6,2,4,6,8};
vector<int> AVec(a,a+sizeof(a)/sizeof(int));
vector<int> BVec(b,b+sizeof(b)/sizeof(int));
vector<int> ans;
cout<<"A:\t";
copy(AVec.begin(), AVec.end(), ostream_iterator<int>(cout," "));
cout<<"\nB:\t";
copy(BVec.begin(), BVec.end(), ostream_iterator<int>(cout," "));
Intersect(AVec,BVec,ans);
cout<<"\nA Intersect B:\n";
copy(ans.begin(), ans.end(), ostream_iterator<int>(cout," "));
ans.clear();
Union(AVec,BVec,ans);
cout<<"\nA Union B:\n";
copy(ans.begin(), ans.end(), ostream_iterator<int>(cout," "));
ans.clear();
Difference(AVec,BVec,ans);
cout<<"\nA - B:\n";
copy(ans.begin(), ans.end(), ostream_iterator<int>(cout," "));