PAT hash算法

#include <iostream>
#include <cstring>
#include <vector>
#include <unordered_map>
using namespace std;

unordered_map<string,bool> visit;

int main()
{
    int m, n;
    cin >> m;
    string str;
    bool flag = true, f1 = true;
    while (m --)
    {

        cin >> str;
        visit[str] = true;
    }
    cin >> n;
    vector<string> a;
    string id_all, id_ali, min, min_aln;
    while (n --)
    {
        cin >> str;
        string sstr = str.substr(6, 8);
        if (flag) min = sstr, flag = false, id_all = str;
        else{
            if (sstr < min) min = sstr, id_all = str;
        }
        if (visit[str])
        {
            a.push_back(sstr);
            if (f1) min_aln = sstr, f1 = false, id_ali = str;
            else
            {
                if (sstr < min_aln) min_aln = sstr, id_ali = str;
            }
        }
    }
    cout << a.size() << "\n";
    if (a.size() > 0) cout << id_ali;
    else cout << id_all;
}