[트리] 백준 1764 듣보잡

#include <iostream>

#include <set>

#include <string>

#include <vector>

#include <algorithm>

using namespace std;

int main(void) {

        set<string> s;

        int a, b;

        cin >> a >> b;

        string input;

        vector<string> output;

        for (int i = 0; i < a; ++i) {

               cin >> input;

               s.insert(input);

        }

        for (int i = 0; i < b; ++i) {

               cin >> input;

               if (s.insert(input).second == false) {

                       output.push_back(input);

               }

        }

        cout << output.size() << endl;

        sort(output.begin(), output.end());

        vector<string>::iterator it;

        for (it = output.begin(); it != output.end(); ++it) {

               cout << *it << endl;

        }

        return 0;

}