Strategy for mutual fans

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ideas

In fact, this question does not require knowledge of graphs at all.
Count the in-degree and out-degree of each point and check the data for duplicates.

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code

#include <iostream>
using namespace std;

int n,m;
int din[1001],dout[1001];
bool vis[1001][1001];

int main(int argc, char const *argv[]) {
    cin>>n>>m;
    for(int i=0;i<m;i++){
        int a,b;
        cin>>a>>b;
        if(!vis[a][b]){
            vis[a][b]=true;
            din[b]++;
            dout[a]++;
        }
    }
    for(int i=0;i<n;i++){
        cout<<din[i]-dout[i]<<endl;
    }

    return 0;
}