C++ 代码

#include <iostream>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
using namespace std;

unordered_map<int, int> mp;
unordered_set<int> party;
int main() {
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        int x1, x2;
        cin >> x1 >> x2;
        mp[x1] = x2;
        mp[x2] = x1;
    }

    int m;
    cin >> m;
    for (int i = 0; i < m; i++) {
        int x;
        cin >> x;
        party.insert(x);
    }
    vector<int> ans;
    for (auto& item : party) {
        //有伴侣，但是没参加聚会
        if (mp.count(item)) {
            if (party.count(mp[item]) == 0) {
                ans.push_back(item);
            }           
        }
        else {
        //无伴侣
            ans.push_back(item);
        }
    }
    printf("%d\n", ans.size());
    sort(ans.begin(), ans.end());
    for (int i = 0; i < ans.size(); i++) {
        if (i) printf(" ");
        printf("%05d", ans[i]);
    }
    return 0;
}