Kill Captain America

                 Kill Captain America
Captain America is hiding from Thanos in a maze full of rooms.
The maze is designed in such a way that the room, within it, leads to another room via gate.

Captain America is hiding only in those rooms which are accessible directly/indirectly through every other room in the maze.

Further provided that, the movement from one room (R1) to another room (R2) is one way(unidirectional) only .
Now, you being on Thanos side, want to kill Captain America.  




#include <bits/stdc++.h>
#define pb push_back
#define endll "\n";
using namespace std;

void dfs(vector<int> adj[],int i,int vis[],stack<int>&s){
    vis[i]=1;
    for(int j=0;j<adj[i].size();j++){
        if(vis[adj[i][j]]==0){
            dfs(adj,adj[i][j],vis,s);
        }
    }
    s.push(i);
}

vector<int> c1;

void dfs1(vector<int> adj[],int i,int vis[] ){
    vis[i]=1;
    for(int j=0;j<adj[i].size();j++){
        if(vis[adj[i][j]]==0){
            dfs1(adj,adj[i][j],vis);
        }
    }
    c1.pb(i);
}


int main()
{
    ios_base::sync_with_stdio(false);cin.tie(NULL);
    int t;cin>>t;
    while(t--){
        int n,e;cin>>n>>e;
        vector<int> adj1[n+1],adj2[n+1];
        int u,v;
        for(int i=0;i<e;i++){
            cin>>u>>v;
            adj1[v].pb(u);
            adj2[u].pb(v);
        }
       
        stack<int> s;
        int vis[n+1];memset(vis,0,sizeof(vis));
        for(int i=1;i<=n;i++){
            if(vis[i]==0){
                dfs(adj1,i,vis,s);
            }
        }
       
        stack<int> s1;memset(vis,0,sizeof(vis));
        c1.clear();
        dfs1(adj2,s.top(),vis);
        if(c1.size()==0){
            cout<<0<<endll;
            continue;
        }
       
        int f=1;
        stack<int> s2;memset(vis,0,sizeof(vis));
        dfs(adj1,c1[0],vis,s2);
        for(int i=1;i<=n;i++){
            if(vis[i]==0){
                f=0;break;
            }
        }
       
        cout<<(f==0?0:c1.size())<<endll;
    }
    return 0;
}