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

//初始化用用-1
//因为有人的编号可能是00000
//所以第二个点不过 
#include<cstdio>
const int maxn = 100010;

int spouse[maxn] = {0};

int main(){
    int n,id1,id2;
    for(int i = 0; i < maxn; i++) spouse[i] = -1; 
    scanf("%d",&n);
    while(n--){
        scanf("%d%d",&id1,&id2);
        spouse[id1] = id2;
        spouse[id2] = id1;  
    }
    scanf("%d",&n);
    while(n--){
        scanf("%d",&id1);
        if(spouse[id1] >= 0 && spouse[spouse[id1]] >= 0){
            spouse[id1] = -2;
        }else if(spouse[id1] >= 0 &&spouse[spouse[id1]] == -2){
            spouse[spouse[id1]] = 2;
        }else{
            spouse[id1] = -3;
        }
    }
    int cnt = 0;
    for(int i = 0; i < maxn; i++){
        if(spouse[i] < -1) cnt++;
    }
    printf("%d\n",cnt);
    for(int i = 0; i < maxn; i++){
        if(spouse[i] < -1){
            printf("%05d",i);
            cnt--;
            if(cnt > 0) printf(" ");
        }    
    }
    return 0;
}