def is_cyclic(directed_graph):
""" Function that checks whether a directed graph contains a cycle or not
Args:
directed_graph (DirectedGraph): The directed graph
Returns:
bool: True if the directed graph contains a cycle, otherwise False
"""
Logging.log("\nStarting cycle check")
traversed_already = dict()
in_cycle = {i:False for i in directed_graph.get_vertices().keys()}
for label, vertex in directed_graph.get_vertices().items():
if traversed_already.get(label) is None:
if is_cyclic_dfs(directed_graph, vertex, traversed_already, in_cycle):
return True
return False
def create_sccs_kosaraju_dfs(directed_graph, nontrivial):
""" Function that creates a list of strongly connected components according to
Kosaraju's algorithm (https://en.wikipedia.org/wiki/Kosaraju%27s_algorithm) with a
depth-first-search approach.
Args:
directed_graph (DirectedGraph): The directed graph for which the SCCS should be calculated
nontrivial(bool): If True, only nontrivial sccs will be returned, otherwise all sccs
Returns:
list(set()) of SCCs: Each SCC is a set of vertices
"""
Logging.log("\nStarting")
stack = []
sccs_trivial, visited = list(), dict()
for vertex in directed_graph.get_vertices().keys():
if visited.get(vertex) is None:
Logging.log("Vertex {0} not visited, go deep", vertex)
kh.fill_order_dfd_sccs(directed_graph, vertex, visited, stack)
else:
Logging.log("Vertex {0} already visited, skipping", vertex)
reversed_graph = get_reversed_graph(directed_graph)
visited = dict()
for i in reversed(stack):
if visited.get(i) is None:
sccs_trivial.append(set())
kh.visit_dfs_sccs(reversed_graph, i, visited, sccs_trivial[-1])
if nontrivial:
return filter_nontrivial(sccs_trivial, directed_graph)
else:
return sccs_trivial
def fill_order_dfd_sccs(directed_graph, vertex, visited, stack):
""" Function that covers the first part of the algorith by determining
the order of vertices, traversing the graph with a depth first search, recursively
Args:
directed_graph (DirectedGraph): The directed graph
vertex: The current vertex
visited (dict): A dictionary that maintains whether vertices have been visisted
stack (list): stack that will be processed, used to inverse the order
"""
visited[vertex] = True
for head in directed_graph.get_vertices()[vertex].get_heads():
Logging.log("Vertex {0}, head {1} in fill order starting", vertex,
head.get_label())
if visited.get(head.get_label()) is None:
Logging.log(
"Vertex {0}, head {1} not visited, go to fill order rec.",
vertex, head.get_label())
Logging.inc_indent()
fill_order_dfd_sccs(directed_graph, head.get_label(), visited,
stack)
Logging.dec_indent()
Logging.log("Vertex {0}, head {1} returned from fill order",
vertex, head.get_label())
Logging.log("Vertex {0}, head {1} in fill order finished", vertex,
head.get_label())
else:
Logging.log("Vertex {0}, head {1} already visited, skipping",
vertex, head.get_label())
Logging.log("Vertex {0}, head {1} in fill order finished", vertex,
head.get_label())
stack = stack.append(vertex)
