def disconnect(self, v, w):
"""Disconnect two vertices."""
if not v in self:
raise ValueError
if not w in self:
raise ValueError
if w == v:
raise ValueError('{} and {} are the same vertex.'.format(v, w))
if not contains(self(v), w):
raise ValueError('{} and {} are not connected.'.format(v, w))
# Only support undirected edges
assert contains(self(w), v)
self.neighborhoods[v] -= w
self.neighborhoods[w] -= v
def components(graph):
"""Return a list of the connected components of in the graph."""
done = 0
for v in iterate(graph.vertices):
if contains(done, v):
continue
component = sum(bfs(graph, v))
yield component
done |= component
def trivial_case(N, left, right, v):
# No neighbors
if contains(left, N[v]):
return True
# Twins
for u in iterate(left):
if N[v] & right == subtract(N[u], v) & right:
return True
return False
def split(self, v, w):
"""Split edge between two vertices."""
if not v in self:
raise ValueError
if not w in self:
raise ValueError
if w == v:
raise ValueError('{} and {} are the same vertex.'.format(v, w))
if contains(self(v), w):
raise ValueError('{} and {} are not connected.'.format(v, w))
# Only support undirected edges
assert contains(self(w), v)
new = bit(size(self.vertices))
self.add(new)
self.disconnect(v, w)
self.connect(v, new)
self.connect(w, new)
def __contains__(self, v):
"""Test if we contain vertex v."""
return contains(self.vertices, v)
