dfw的我来一个map的，也不需要遍历容器。

#include <iostream>
#include <cstring>
#include <algorithm>
#include <unordered_map>
using namespace std;
unordered_map<string, int> schoolmate;
int n, m;
int cnt;
int main()
{
    cin >> n;
    while(n--){
        string id;
        cin >> id;
        schoolmate[id] = 1;
    }
    cin >> m;
    string max_schoolmate, max_com;
    string max_age_schoolmate ="99999999";
    string max_age_com = "99999999";
    while (m -- ){
        string com_id;
        string age;
        cin >> com_id;
        age = com_id.substr(6, 8);
        if(age < max_age_com){
            max_com = com_id;
            max_age_com = age;
        }
        auto iter = schoolmate.find(com_id);
        if(iter != schoolmate.end()){
            cnt++;
            if(age < max_age_schoolmate){
                max_schoolmate = com_id;
                max_age_schoolmate = age;
            }

        }
    }

    if(cnt){
        cout << cnt << endl;
        cout << max_schoolmate << endl;

    }else{
        cout << cnt << endl;
        cout << max_com << endl;
    }

    return 0;
}