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[100005], flag[100005];
    set<int>guests, res;
    cin >> n;
    fill(couple, couple + 100005, -1);
    fill(flag, flag + 100005, 0);
    while (n--)
    {
        cin >> boy >> girl;
        couple[boy] = girl;
        couple[girl] = boy;
    }
    cin >> m;
    while (m--)
    {
        cin >> id;
        guests.insert(id);
        if (couple[id] == -1)
            continue;
        else if (flag[id] == 0)//对偶没有来
        {
            flag[id] = 1;
            flag[couple[id]] = 1;
        }
        else if (flag[id] == 1)//对偶来了
        {
            flag[id] = -1;
            flag[couple[id]] = -1;
        }
    }
    for (auto a : guests)
    {
        if (flag[a] != -1)
            res.insert(a);
    }
    cout << res.size() << endl;
    for (auto a : res)
        printf("%s%05d", (a == *(res.begin()) ? "" : " "), a);
    return 0;
}