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#
# Copyright (C) 2015 FreeIPA Contributors see COPYING for license
#
class Graph():
"""
Simple oriented graph structure
G = (V, E) where G is graph, V set of vertices and E list of edges.
E = (tail, head) where tail and head are vertices
"""
def __init__(self):
self.vertices = set()
self.edges = []
self._adj = dict()
def add_vertex(self, vertex):
self.vertices.add(vertex)
self._adj[vertex] = []
def add_edge(self, tail, head):
if tail not in self.vertices:
raise ValueError("tail is not a vertex")
if head not in self.vertices:
raise ValueError("head is not a vertex")
self.edges.append((tail, head))
self._adj[tail].append(head)
def remove_edge(self, tail, head):
try:
self.edges.remove((tail, head))
except KeyError:
raise ValueError(
"graph does not contain edge: (%s, %s)" % (tail, head))
self._adj[tail].remove(head)
def remove_vertex(self, vertex):
try:
self.vertices.remove(vertex)
except KeyError:
raise ValueError("graph does not contain vertex: %s" % vertex)
# delete _adjacencies
del self._adj[vertex]
for key, _adj in self._adj.items():
_adj[:] = [v for v in _adj if v != vertex]
# delete edges
edges = [e for e in self.edges if e[0] != vertex and e[1] != vertex]
self.edges[:] = edges
def get_tails(self, head):
"""
Get list of vertices where a vertex is on the right side of an edge
"""
return [e[0] for e in self.edges if e[1] == head]
def get_heads(self, tail):
"""
Get list of vertices where a vertex is on the left side of an edge
"""
return [e[1] for e in self.edges if e[0] == tail]
def bfs(self, start=None):
"""
Breadth-first search traversal of the graph from `start` vertex.
Return a set of all visited vertices
"""
if not start:
start = list(self.vertices)[0]
visited = set()
queue = [start]
while queue:
vertex = queue.pop(0)
if vertex not in visited:
visited.add(vertex)
queue.extend(set(self._adj.get(vertex, [])) - visited)
return visited
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