1121 Damn Single (25分)

"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

单身狗，我们给定一些夫妻，给定一些人员，把单身狗打印。（也要把我打印QAQ）

#include <iostream>
#include <unordered_map>
#include <set>
using namespace std;
int N, M, a, b;
unordered_map<int, set<int>> s;
set<int> query;
int main() {
    scanf("%d", &N);
    while(N--) {
        scanf("%d%d", &a, &b);
        s[a].insert(b);
        s[b].insert(a);
    }
    scanf("%d", &M);
    while(M--) {
        scanf("%d", &a);
        query.insert(a);
    }
    for(auto& x: s) {
        auto it = query.find(x.first);
        if(it == query.end()) continue;
        for(auto& y: s[x.first]) {
            auto it2 = query.find(y);
            if(it2 != query.end()) {
                query.erase(it);
                query.erase(it2);
                break;
            }
        }
    }
    printf("%lu\n", query.size());
    bool start = true;
    for(auto& x: query) {
        if(start == true) {
            printf("%05d", x);
            start = false;
        } else printf(" %05d", x);
    }
    return 0;
}