1121 Damn Single

"Damn Single (单身狗)" is the Chinese nickname for someone who is being single. You are supposed to find those who are alone in a big party, so they can be taken care of.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤ 50,000), the total number of couples. Then N lines of the couples follow, each gives a couple of ID's which are 5-digit numbers (i.e. from 00000 to 99999). After the list of couples, there is a positive integer M (≤ 10,000) followed by M ID's of the party guests. The numbers are separated by spaces. It is guaranteed that nobody is having bigamous marriage (重婚) or dangling with more than one companion.

Output Specification:

First print in a line the total number of lonely guests. Then in the next line, print their ID's in increasing order. The numbers must be separated by exactly 1 space, and there must be no extra space at the end of the line.

Sample Input:

3
11111 22222
33333 44444
55555 66666
7
55555 44444 10000 88888 22222 11111 23333

Sample Output:

5
10000 23333 44444 55555 88888

#include 
#include 
#include 
using namespace std;
int n, m, a[100010], x, y, b[100010], ans, cnt, c[100010];
bool couple[100010], vis[100010];
 
int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x >> y;
		a[x] = y;
		a[y] = x;
		couple[x] = 1;
		couple[y] = 1;
	}
	cin >> m;
	for (int i = 0; i < m; i++) {
		cin >> b[i];
		vis[b[i]] = 1;
	}
	for (int i = 0; i < m; i++) {
		if (!couple[b[i]]) { //本来就是单身
			c[cnt++] = b[i];
		} else {
			if (!vis[a[b[i]]]) {
				c[cnt++] = b[i]; //伴侣没来
			}
		}
	}
	sort(c, c + cnt);
	cout << cnt << endl;
	for (int i = 0; i < cnt; i++) {
		cout << setw(5) << setfill('0') << c[i];
		if (i != cnt - 1) {
			cout << ' ';
		}
	}
	return 0;
}