Python DC.hasCycle Examples

Example #1

File: Topological.py Project: thecocce/Algorithms-Python

	def __init__(self, G):
		"sorts the vertices of G in reverse DFS postorder"
		self._order = []
		# determine whether G is a digraph or edge-weighted digraph
		if isinstance(G, Digraph):
			finder = DC(G)
		else:
			finder = EdgeWeightedDC(G)
		
		assert not finder.hasCycle(), "graph is not acyclic"
		dfs = DFOrder(G)
		self._order = dfs.reversePost()

Example #2

File: Reachable.py Project: thecocce/Algorithms-Python

	def __init__(self, G):
		self._all_marked_lists = []
		dc = DC(G)
		if dc.hasCycle():
			# digraph with cycle
			for v in range(G.V()):
				self._marked = [False for _ in range(G.V())]
				self._dfs(G, v)
				self._all_marked_lists.append(self._marked)
			# done running DFS on vertices; find intersection of all marked lists
			all_lists = [[i for i in range(G.V()) if alist[i] is True] for alist in self._all_marked_lists]
			final = set(all_lists[0])
			for s in all_lists[1:]:
				ss = set(s)
				final = final.intersection(ss)
			if not final:
				print "no vertex is reachable from all other vertices"
			else:
				for i in final:
					print i
		else:
			# DAG
			# only the target vertex is a candidate for being reachable
			dfs = DFOrder(G)
			reverse_post = dfs.reversePost()
			target = reverse_post[-1]
			for v in reverse_post:
				if v != target:
					self._marked = [False for _ in range(G.V())]
					self._dfs(G, v)
					self._all_marked_lists.append(set(self._marked))
			# done running DFS on vertices; target must be in all marked lists
			for markedList in self._all_marked_lists:
				if target not in markedList:
					print "no vertex is reachable from all other vertices"
					return
			print target