Shared code

#include<iostream>
#include<vector>
#include<stack>
#include<algorithm>
using namespace std;
class FlightRoutesCheck{
  vector<int>*graph,*flipGraph;
  vector<bool>vis;
  vector<int>ans;
  stack<int>st;
public:
  FlightRoutesCheck(vector<int> *g,vector<int>*f,int n){
     graph=g;
     flipGraph=f;
     vis.resize(n+1,false);
  }
  void traverse(int u){
    if(vis[u])return;
    vis[u]=true;
    for(int v:graph[u]){
      traverse(v);
    }
    st.push(u);
  }
  void revTraverse(int u){
   if(vis[u])return;
    vis[u]=true;
    for(int v:flipGraph[u]){
      revTraverse(v);
    } 
  }
  vector<int> getSol(int n){
    for(int i=1;i<=n;i++){
      if(!vis[i]){
        traverse(i);
      }
    }
    fill(vis.begin(),vis.end(),false);
    int num;
    while(!st.empty()){
      num=st.top();
      st.pop();
      if(!vis[num]){
        revTraverse(num);
        ans.push_back(num);
      }
      if(ans.size()==2)break;
    }
    return ans;
  }
};
int main(){
   int n,m,a,b;
   cin>>n>>m;
   vector<int> graph[n+1],flipGraph[n+1];
   for(int i=0;i<m;i++){
      cin>>a>>b;
      graph[a].push_back(b);
      flipGraph[b].push_back(a);
   }
   FlightRoutesCheck check(graph,flipGraph,n);
  vector<int> ans=check.getSol(n);
  if(ans.size()==2){
    cout<<"NO\n"<<ans[1]<<" "<<ans[0];
  }else{
    cout<<"YES\n";
  }
  return 0;
}