solution

• “单身狗”：没有搭子或者搭子没来的参与者
• 输出id时按增序输出

#include<iostream>
#include<map>
#include<algorithm>
using namespace std;
const int maxn = 1e6, maxn1 = 1e4 + 10;
int flag[maxn] = {0}, all[maxn1];
int main(){
	int n, m, cp1, cp2, cnt = 0, x;
	map<int, int> mp;
	scanf("%d", &n);
	for(int i = 0; i < n; i++){
		scanf("%d%d", &cp1, &cp2);
		mp[cp1] = cp2;
		mp[cp2] = cp1;
	}
	scanf("%d", &m);
	for(int i = 0; i < m; i++){
		scanf("%d", all + i);
		flag[all[i]] = 1;
	}
	for(int i = 0; i < m; i++){
		if(mp.count(all[i]) && flag[mp[all[i]]]) continue;
		all[cnt++] = all[i];
	}
	sort(all, all + cnt);
	printf("%d\n", cnt);
	for(int i = 0; i < cnt; i++){
		printf("%05d", all[i]);
		if(i != cnt - 1) printf(" ");
	}
	return 0;
}