def BFS(G,root,direction='forward'):
""" Calculate BFS distances and predecessor without showing animations.
If G is directed, direction does matter:
- 'forward' BFS will use outgoing edges
- 'backward' BFS will use incoming edges
It uses gInfinity (from GatoGlobals.py) as infinite distance.
returns (dist,pred) """
Q = Queue()
d = {}
pred = {}
for v in G.vertices:
d[v] = gInfinity
d[root] = 0
pred[root] = root
Q.Append(root)
while Q.IsNotEmpty():
v = Q.Top()
if G.QDirected() == 1 and direction == 'backward':
nbh = G.InNeighbors(v)
else:
nbh = G.Neighborhood(v)
for w in nbh:
if d[w] == gInfinity:
d[w] = d[v] + 1
pred[w] = v
Q.Append(w)
return (d,pred)
def ConnectedComponents(G):
""" Compute the connected components of the undirected graph G.
Returns a list of lists of vertices. """
result = []
visited = {}
for v in G.vertices:
visited[v] = None
for root in G.vertices:
if visited[root] is not None:
continue
else: # Found a new component
component = [root]
visited[root] = 1
Q = Queue()
Q.Append(root)
while Q.IsNotEmpty():
v = Q.Top()
nbh = G.Neighborhood(v)
for w in nbh:
if visited[w] == None:
visited[w] = 1
Q.Append(w)
component.append(w)
result.append(component)
return result
def FindBipartitePartitions(G):
""" Finds the two partitions of a bipartite graph G and returns
two vertex sets. If G is not bipartite, it returns two empty
sets.
"""
Q = Queue()
V = set()
W = set()
dist = {}
for v in G.vertices:
if v not in dist:
dist[v] = 0
Q.Append(v)
V.add(v)
while Q.IsNotEmpty():
v = Q.Top()
for w in G.Neighborhood(v):
if w not in dist:
dist[w] = dist[v] + 1
Q.Append(w)
if dist[w] % 2 == 1:
W.add(w)
else:
V.add(w)
else:
if (dist[w] + dist[v]) % 2 == 0:
# Found an incompatible edge
return (set(), set())
return (V, W)
def RadialTreeBFS(G,root,direction='forward'):
""" Calculate BFS distances and predecessor without showing animations.
Also compute angles for a radial layout
If G is directed, direction does matter:
- 'forward' BFS will use outgoing edges
- 'backward' BFS will use incoming edges
It uses gInfinity (from GatoGlobals.py) as infinite distance.
returns (dist,pred) """
Q = Queue()
d = {}
pred = {}
angle = {}
childrenrange = {}
for v in G.vertices:
d[v] = gInfinity
d[root] = 0
pred[root] = None
angle[root] = 0
childrenrange[root] = (0, 2 * pi)
Q.Append(root)
while Q.IsNotEmpty():
v = Q.Top()
if G.QDirected() == 1 and direction == 'backward':
nbh = G.InNeighbors(v)
else:
nbh = G.Neighborhood(v)
# Compute size of unseen Nbh
unseen = 0
for w in nbh:
if d[w] == gInfinity:
unseen += 1
if unseen > 0:
range = childrenrange[v][1] - childrenrange[v][0]
delta = range / float(unseen)
delta2 = delta * 0.5
left = childrenrange[v][0] + delta2
for w in nbh:
if d[w] == gInfinity:
angle[w] = left + delta2
childrenrange[w] = (left,left+delta)
left += delta
d[w] = d[v] + 1
#print (v,w), "angle = ", angle[w]," range = ", childrenrange[w]
Q.Append(w)
return (d,pred,angle)