PAT甲级——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 (≤ 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

使用couple记录是否有配偶
使用flag标记是否配偶到场
注意：最后不要输出换行，不然一旦没有输出，那么就有两个换行了！

 #include <iostream>
 #include <set>
 using namespace std;
 int main()
 {
     int n, m, boy, girl, id;
     int couple[], flag[];
     set<int>guests, res;
     cin >> n;
     fill(couple, couple + , -);
     fill(flag, flag + , );
     while (n--)
     {
         cin >> boy >> girl;
         couple[boy] = girl;
         couple[girl] = boy;
     }
     cin >> m;
     while (m--)
     {
         cin >> id;
         guests.insert(id);
         if (couple[id] == -)
             continue;
         else if (flag[id] == )//对偶没有来
         {
             flag[id] = ;
             flag[couple[id]] = ;
         }
         else if (flag[id] == )//对偶来了
         {
             flag[id] = -;
             flag[couple[id]] = -;
         }
     }
     for (auto a : guests)
     {
         if (flag[a] != -)
             res.insert(a);
     }
     cout << res.size() << endl;
     for (auto a : res)
         printf("%s%05d", (a == *(res.begin()) ? "" : " "), a);
     return ;
 }