vector<string> lst = { "andrew", "bob", "chris", "bob" };
vector<string> lst_no_dups;
vector<string> tmp;
vector<string> dups;

sort(lst.begin(), lst.end());
unique_copy(lst.begin(), lst.end(), back_inserter(lst_no_dups));
set_difference(lst.begin(), lst.end(),
lst_no_dups.begin(), lst_no_dups.end(),
back_inserter(tmp));
unique_copy(tmp.begin(), tmp.end(), back_inserter(dups));

cout << dups << endl;

#include <algorithm>
#include <iostream>
#include <iterator>
#include <list>
#include <vector>

using namespace std;

template<typename T>
ostream& operator<<(ostream &os, const vector<T> &l)
{
os << "[ ";
copy(l.begin(), l.end(), ostream_iterator<T>(os, " "));
os << "]";
return os;
}

int main()
{
// It is only the initialization of 'lst' that requires C++0x/C++11 rest works with C++98
vector<string> lst = { "andrew", "bob", "chris", "bob" };
vector<string> lst_no_dups;
vector<string> tmp;
vector<string> dups;

sort(lst.begin(), lst.end());
unique_copy(lst.begin(), lst.end(), back_inserter(lst_no_dups));
set_difference(lst.begin(), lst.end(),
lst_no_dups.begin(), lst_no_dups.end(),
back_inserter(tmp));
unique_copy(tmp.begin(), tmp.end(), back_inserter(dups));

cout << dups << endl;
}

list<string> lst = { "andrew", "bob", "chris", "bob" };
map<string,int> num_identical;
list<string> dups;

for (auto &s: lst)
num_identical[s]++;
for (auto &n: num_identical)
if (n.second > 1)
dups.push_back(n.first);
cout << dups << endl;

#include <algorithm>
#include <iostream>
#include <iterator>
#include <list>
#include <map>

using namespace std;

template<typename T>
ostream& operator<<(ostream &os, const list<T> &l)
{
os << "[ ";
copy(l.begin(), l.end(), ostream_iterator<T>(os, " "));
os << "]";
return os;
}

int main()
{
list<string> lst = { "andrew", "bob", "chris", "bob" };
map<string,int> num_identical;
list<string> dups;

for (auto &s: lst)
num_identical[s]++;
for (auto &n: num_identical)
if (n.second > 1)
dups.push_back(n.first);
cout << dups << endl;

}