Topology sort Kahn's algorithm

void Graph::topologicalSort()
{
    vector<int> in_degree(V, 0);

    for (int u=0; u<V; u++)
    {
        list<int>::iterator itr;
        for (itr = adj[u].begin(); itr != adj[u].end(); itr++)
             in_degree[*itr]++;
    }

    queue<int> q;
    for (int i = 0; i < V; i++)
        if (in_degree[i] == 0)
            q.push(i);

    int cnt = 0;

    vector <int> top_order;

    while (!q.empty())
    {
        int u = q.front();
        q.pop();
        top_order.push_back(u);

        list<int>::iterator itr;
        for (itr = adj[u].begin(); itr != adj[u].end(); itr++)
            if (--in_degree[*itr] == 0)
                q.push(*itr);
        cnt++;
    }

    // Check if there was a cycle
    if (cnt != V)
    {
        cout << "There exists a cycle in the graph\n";
        return;
    }

    // Print topological order
    for (int i=0; i<top_order.size(); i++)
        cout << top_order[i] << " ";
    cout << endl;
}