For a directed acyclic graph(DAG) G = (V, E), topological sort is a sort for all of node in G. The order should be:

• if Gragh G contains (u,v) edge, then node u in topological sort should be at the former of node v.

Pseudocode

// TOPOLOGICAL-SORT(G)
call DFS(G) to compute finishing times v.f for each vertex v
as each vertex is finished, insert it onto the front of a linked list
return the linked list of vertices

We could implement it in O(V+E) <- which is the DFS time complexity.