Maximum edges that can be added to DAG so that it remains DAG 连通性

Maximum edges that can be added to DAG so that it remains DAG - GeeksforGeeks https://www.geeksforgeeks.org/maximum-edges-can-added-dag-remains-dag/

A DAG is given to us, we need to find maximum number of edges that can be added to this DAG, after which new graph still remain a DAG that means the reformed graph should have maximal number of edges, adding even single edge will create a cycle in graph.