Topological sort using Kahn's algorithm

  vector<int> topological_sorting(vector<vector<int>> graph) {
    vector <int> indegree(graph.size(), 0);
    queue<int> q;
    vector<int> solution;
    
    for(int i = 0; i < graph.size(); i++) {
        for(int j = 0; j < graph[i].size(); j++)
        { 
        //iterate over all edges
            indegree[ graph[i][j] ]++;
        }
    }
    
    //enqueue all nodes with indegree 0
    for(int i = 0; i < graph.size(); i++) 
    {
        if(indegree[i] == 0) {
            q.push(i);
        }
    }

    //remove one node after the other
    while(q.size() > 0) {
        int currentNode = q.front();
        q.pop();
        solution.push_back(currentNode);
        for(int j = 0; j < graph[currentNode].size(); j++)
        { 
        //remove all edges
            int newNode = graph[currentNode][j];
            indegree[newNode]--;
            if(indegree[newNode] == 0) 
            { 
            //target node has now no more incoming edges
                q.push(newNode);
            }
        }
    }
    
    return solution;
}
int main() 
{ 
	
	int n,v1,v2;
	cin>>n;
	vector<vector<int>> graph;
	for(int i=1;i<=n;i++)
        {
            cin>>v1>>v2;
	    g.addEdge(v1, v2);
        } 
	

	cout << " Topological Sort of the given graph \n"; 
	g.topologicalSort(); 

	return 0; 
}