PAT 1121 Damn Single[简单]

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

题目大意：给出n对情侣，然后再给出m对参加宴会的人，判断这些人当中有多少人是没有伙伴来参加宴会的（本身已经结婚，但是没带伴侣来的也会被计算进来）

#include <iostream>

#include<vector>

#include<map>

using namespace std;

map<string,string> m2f;

map<string,string> inp;

int main() {

    int n;

    cin>>n;

    string x,y;

    for(int i=;i<n;i++){

        cin>>x>>y;

        m2f[x]=y;

        m2f[y]=x;

    }

    int m;

    cin>>m;

    string s;

    for(int i=;i<m;i++){

        cin>>s;

        inp[s]=;//因为这里的map是自然排序的，所以最终vector里也是自然排序的。

    }

    int ct=;

    vector<string> vt;

    for(auto it=inp.begin();it!=inp.end();it++){

        string str=it->first;

        if(inp.count(m2f[str])==){

            vt.push_back(str);

        }

    }

    cout<<vt.size()<<'\n';

    for(int i=;i<vt.size();i++){

        cout<<vt[i];

        if(i!=vt.size()-)cout<<" ";

    }

    return ;

}

//还是比较简单的，但是还是提交了两次，为什么呢？

1.需要主要最后的输出格式，是1!=vt.size()-1，知道了吗？

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