def __init__(self, G): # G is Digraph O(V+E) wc
finder = DirectedCycle(G)
if not finder.hasCycle():
dfs = DepthFirstOrder(G)
self._order = dfs.reversePost() # topological order
self._rank = [] # rank[v] = position of vertex v in topological order
i = 0
for v in self. order:
self._rank[v] = i
i += 1
def Topological(EdgeWeightedDigraph G): # EdgeWeightedDigraph
"""Determines if digraph G has a topological order and, if so, finds topological order."""
EdgeWeightedDirectedCycle finder = new EdgeWeightedDirectedCycle(G)
if not finder.hasCycle():
dfs = DepthFirstOrder(G)
order = dfs.reversePost()
