[백준]1764 - 듣보잡(설명X)

#include <iostream>
#include <string>
#include <set>
#include <list>
using namespace std;
 
int main() {
    set<string> n_set;
    list<string> dup;
    int N, M;
    cin >> N >> M;
    
    for (int i = 0; i < N; i++) {
        string str;
        cin >> str;
        n_set.insert(str);
    }
 
    for (int i = 0; i < M; i++) {
        string str;
        cin >> str;
        if (n_set.find(str) != n_set.end())
            dup.push_back(str);
    }
 
    dup.sort();
    cout << dup.size() << endl;
    list<string>::iterator iter;
    for (iter = dup.begin(); iter != dup.end(); iter++)
        cout << *iter << endl;
}