哈希表，使用set自动排序

C++ 代码

#include <iostream>
#include <set>
#include <unordered_map>
using namespace std;
int m, n;

int main(){
    unordered_map<string, string> couple;
    set<string> people, people1;
    cin >> m;
    for(int i = 0; i < m; ++ i) {
        string m, f;
        cin >> m >> f;
        couple[m] = f;
        couple[f] = m;
    }
    cin >> n;
    for(int i = 0; i < n; ++ i){
        string s;
        cin >> s;
        people.insert(s);
    }
    people1 = people;
    for(auto& x : people1){
        if(couple.count(x) == 1 && people1.count(couple[x]) == 1){
            people.erase(x);
            people.erase(couple[x]);
        }
    }
    cout << people.size() << endl;
    for(auto& x : people)
        cout << x << ' ';
    return 0;
}