def get_sink(G: WeightedDirectedGraph) -> int:
"""
Return index of output vertex in graph G
Example:
>>> get_sink(WeightedDirectedGraph.fromfile(open('wiki_flow.txt')))
5
>>> get_sink(WeightedDirectedGraph(0,0,[]))
Traceback (most recent call last):
...
algorithm.no_sink
>>> get_sink(WeightedDirectedGraph(3,2,
... [WeightedDirectedEdge(0, 1, 1), WeightedDirectedEdge(0, 2, 1)]))
Traceback (most recent call last):
...
algorithm.ambigous_sink
"""
V = [v for v in range(G.V()) if len(G.adj(v)) == 0]
if not V:
raise no_sink
if len(V) > 1:
raise ambigous_sink
return V[0]
