#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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