#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
#include <set>
using namespace std;
 
int main(int argc,char *argv[])
  {
   vector<string> a { "aaa","xxx","bbb","ccc"};
   vector<string> b { "aaa","bbb","yyy","ccc"};
   set<string> ab(a.begin(),a.end());
   for(auto s:b) ab.erase(s);
   set<string> ba(b.begin(),b.end());
   for(auto s:a) ba.erase(s);
   for(auto s:ba) ab.insert(s);
   copy(ab.begin(),ab.end(),ostream_iterator<string>(cout," "));
   return 0;
  }

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