Prerequisite_tasks.cpp

//{ Driver Code Starts
#include<bits/stdc++.h>
using namespace std;

// } Driver Code Ends
class Solution {
public:
	bool isPossible(int V, int P, vector<pair<int, int> >& prerequisites) {
	    vector<int> adj[V];
	    
	    for(auto it : prerequisites)
	    {
	        adj[it.first].push_back(it.second);
	    }
	    
	    int indegree[V] = {0};
        
        for(int i = 0; i < V; i++)
        {
            for(auto it : adj[i])
                indegree[it]++;
        }
        
        queue<int>q;
        for(int i = 0; i < V; i++)
        {
            if(indegree[i] == 0)
                q.push(i);
        }
        int cnt = 0;
        while(!q.empty())
        {
            int node = q.front();
            q.pop();
            cnt++;
            for(auto it : adj[node])
            {
                indegree[it]--;
                if(indegree[it] == 0) q.push(it);
            }
        }
        return cnt == V;
    }
};

//{ Driver Code Starts.
int main(){
	int tc;
	cin >> tc;
	while(tc--){
    	int N, P;
        vector<pair<int, int> > prerequisites;
        cin >> N;
        cin >> P;
        for (int i = 0; i < P; ++i) {
            int x, y;
            cin >> x >> y;
            prerequisites.push_back(make_pair(x, y));
        }
        // string s;
        // cin>>s;
        Solution ob;
        if (ob.isPossible(N,P, prerequisites))
            cout << "Yes";
        else
            cout << "No";
        cout << endl;
	}
	return 0;
}
// } Driver Code Ends