Topological Sorting

Topological Sorting.py

Let L be an empty list
Let all vertices be initially unmarked

while there are unmarked vertices:
  select an unmarked vertex u
  dfs(u)

def dfs(vertex u):
  mark u
  foreach edge u -> v
    if v is unmarked:
      dfs(v)
  add u to head of L

L represents the topological order of the DAG