***還是比較簡單的，問題在於最後輸出時如果是4位數，應當輸出前置的0，這一點不注意的話，有一個點始終過不去*。**
#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <iomanip>
using namespace std;

int main()
{
    map<int,int> A;
    int N;
    cin >> N;
    //這是夫妻的map
    for (int i= 0
 
; i < N; i++)
    {
        int f,q;
        cin >> f>>q;
        A.insert({ f,q });
    }
    int M;
    cin >> M;
    vector<int> B;
    for (int i = 0; i < M; i++)
    {
        int num;
        cin >> num;
        B.push_back(num);
    }
    vector<int> C;
    for
 
 (int i = 0; i < B.size(); i++)
    {
        if (A.find(B[i]) != A.end())
        {
            if(find(B.begin(),B.end(), A.at(B[i]))!=B.end())
            {
                C.push_back(B[i]);
                C.push_back(A.at(B[i]));
            }
        }
    }
    sort(B.begin(), B.end());
    sort(C.begin(), C.end());
    vector
 
<int> D(B.size()-C.size());
    set_difference(B.begin(), B.end(), C.begin(), C.end(), D.begin());
    sort(D.begin(), D.end());
    cout << D.size()<<endl;
    for (int i = 0; i < D.size(); i++)
    {
        //printf("%05d", D[i]);
        cout<< setfill('0');
        cout << setw(5) << D[i];
        if (i != D.size() - 1)
            cout << " ";
    }
    return 0;
}