topological sort BFS (Kahn algo) + (cycle detection in DAG)

// removing elements starting from indegree 0 till all are removed.. if count_of_removed elements = vertices .. no cycle exists

vector<int> topoSort(int V, vector<int> adj[])
    {
        int indeg[V];
        for(int a=0;a<V;a++){
            for(int x : adj[a]){
                indeg[x]++;
            }
        }
        queue<int> q;
        for(int a=0;a<V;a++){
            if(indeg[a] == 0){
                q.push(a);
            }
        }
        vector<int> topo;
        int count =0;// visited nodes
        while(!q.empty()){
            int top = q.front();
            q.pop();
            topo.push_back(top);
            count ++;

            for(int x : adj[top]){
                indeg[x]--; // because we removed element with indegree 0 (at q.front())
                if(indeg[x] == 0)q.push(x);
            }
        }
        if(count != V) return {}; // cycle exists

        return topo ;
    }