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

#include<bits/stdc++.h>
using namespace std;
const int maxn=1000010;
map<int,int> mp;
set<int> s;

int main(){
    int n,k,a,b;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>a>>b;
        mp[a]=b;
        mp[b]=a;
    }
    cin>>k;
    int temp;
    for(int i=0;i<k;i++){
        cin>>temp;
        s.insert(temp);
    }
    vector<int> v;
    for(set<int>::iterator it=s.begin();it!=s.end();it++){
        if(s.find(mp[*it])==s.end()){
            v.push_back(*it);
        }
    }
    printf("%d\n",v.size());
    for(int i=0;i<v.size();i++){
        if(i<v.size()-1){
            printf("%05d ",v[i]);
        }
        else{
            printf("%05d\n",v[i]);
        }
    }
    return 0;
}