Question 247. 2022 Winter Holiday Ladder Training - 7-10 Singles (25 points)

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Question 247. 2022 Winter Holiday Ladder Training - 7-10 Singles (25 points)

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1. The topic

2. Problem solving

//我要提醒自己，不是有配对的人就一定不落单的，它另一半可能不来啊！！！
#include <bits/stdc++.h>

using namespace std;

const int maxn=1e5+1;

int cp[maxn];
set<int> s;
vector<int> res;

int main()
{
    
    
    int N;
    cin>>N;
    for(int i=0;i<N;i++)
    {
    
    
        int id1,id2;
        cin>>id1>>id2;
        cp[id1]=id2;
        cp[id2]=id1;
    }
    int M;
    cin>>M;
    for(int i=0;i<M;i++)
    {
    
    
        int id;
        cin>>id;
        s.insert(id);
    }
    for(auto it=s.begin();it!=s.end();it++)
    {
    
    
        if(s.find(cp[*it])==s.end())
        {
    
    
            res.push_back(*it);
        }
    }
    cout<<res.size()<<endl;
    for(int i=0;i<res.size();i++)
    {
    
    
        if(i>0)
        {
    
    
            putchar(' ');
        }
        printf("%05d",res[i]);
    }
}

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