PAT甲级 1121 Damn Single (25 分)

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本文介绍了一种算法，用于从参加派对的嘉宾中识别并统计单身人士的数量及其ID。该算法首先建立夫妻配对关系数据库，然后通过查询嘉宾列表来找出没有配对记录的单身嘉宾。

“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 <cstdio>
#include <vector>
#include <algorithm>
#include <cstring>

using namespace std;
int couple[100000];
bool hashtable[100000] = {false};
int querry[10000];

int main() {
    int N, M, left, right;
    memset(couple, -1, sizeof couple);
    vector<int> v;
    scanf("%d", &N);
    for (int i = 0; i < N; ++i) {
        scanf("%d %d", &left, &right);
        couple[left] = right;
        couple[right] = left;
    }
    scanf("%d", &M);
    for (int i = 0; i < M; ++i) {
        scanf("%d", &querry[i]);
        hashtable[querry[i]] = true;
    }
    for (int i = 0; i < M; ++i) {
        if (!hashtable[couple[querry[i]]])
            v.push_back(querry[i]);
    }
    sort(v.begin(), v.end());
    printf("%d\n", v.size());
    for (int i = 0; i < v.size(); ++i) {
        if (i)
            printf(" %05d", v[i]);
        else
            printf("%05d", v[i]);
    }
    return 0;
}