PAT A1121 . Damn Single (25)

“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 (<=50000), 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 (<=10000) 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

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#include <cstdio>
#include <set>
#include <vector>
using namespace std;
int main() {
int n, a, b, m;
scanf("%d", &n);
vector<int> couple(100000);
for (int i = 0; i < 100000; i++)
couple[i] = -1;
for (int i = 0; i < n; i++) {
scanf("%d%d", &a, &b);
couple[a] = b;
couple[b] = a;
}
scanf("%d", &m);
vector<int> guest(m), isExist(100000);
for (int i = 0; i < m; i++) {
scanf("%d", &guest[i]);
if (couple[guest[i]] != -1) {
isExist[couple[guest[i]]] = 1;
}
}
set<int> s;
for (int i = 0; i < m; i++) {
if (!isExist[guest[i]]) {
s.insert(guest[i]);
}
}
printf("%d\n", s.size());
for (set<int>::iterator it = s.begin(); it != s.end(); it++) {
if (it != s.begin())
printf(" ");
printf("%05d", *it);
}
return 0;
}