def dfs(self,
vertex_set=None,
raise_if_cyclic=False,
enter_vertex=None,
leave_vertex=None):
""" dfs(self,vertex_set=None,raise_if_cyclic=False,enter_vertex=None,
leave_vertex=None) -> (discovery, parent, finish)
Performs a depth-first search on a graph and returns three dictionaries with
relevant information. If vertex_set is not None, then it is used as
the list of ids to perform the DFS on.
See CLRS p. 541.
enter_vertex, when present, is called just before visiting a vertex
for the first time (and only once) with the vertex id as a parameter.
leave_vertex, when present, is called just after visiting a vertex
for the first time (and only once) with the vertex id as a parameter.
"""
if not vertex_set:
vertex_set = self.vertices
# Ugly ugly python
# http://mail.python.org/pipermail/python-list/2006-April/378964.html
# We cannot explicitly "del data":
# http://www.python.org/dev/peps/pep-0227/
class Closure(object):
def clear(self):
del self.discovery
del self.parent
del self.finish
del self.t
# Straight CLRS p.541
data = Closure()
data.discovery = {} # d in CLRS
data.parent = {} # \pi in CLRS
data.finish = {} # f in CLRS
data.t = 0
(enter, leave, back, other) = xrange(4)
# inspired by http://www.ics.uci.edu/~eppstein/PADS/DFS.py
def handle(v, w, edgetype):
data.t += 1
if edgetype == enter:
data.discovery[v] = data.t
if enter_vertex:
enter_vertex(w)
if v != w:
data.parent[w] = v
elif edgetype == leave:
data.finish[w] = data.t
if leave_vertex:
leave_vertex(w)
elif edgetype == back and raise_if_cyclic:
raise self.GraphContainsCycles(v, w)
visited = set()
gray = set()
# helper function to build stack structure
def st(v): return (v, iter(self.adjacency_list[v]))
for vertex in vertex_set:
if vertex not in visited:
handle(vertex, vertex, enter)
visited.add(vertex)
stack = Stack()
stack.push(st(vertex))
gray.add(vertex)
while stack.size:
parent, children = stack.top()
try:
child, _ = children.next()
if child in visited:
handle(parent, child, (child in gray
and back
or other))
else:
handle(parent, child, enter)
visited.add(child)
stack.push(st(child))
gray.add(child)
except StopIteration:
gray.remove(parent)
stack.pop()
if stack.size:
handle(stack.top()[0], parent, leave)
handle(vertex, vertex, leave)
result = (data.discovery, data.parent, data.finish)
data.clear()
return result
def dfs(self,
vertex_set=None,
raise_if_cyclic=False,
enter_vertex=None,
leave_vertex=None):
""" dfs(self,vertex_set=None,raise_if_cyclic=False,enter_vertex=None,
leave_vertex=None) -> (discovery, parent, finish)
Performs a depth-first search on a graph and returns three dictionaries with
relevant information. If vertex_set is not None, then it is used as
the list of ids to perform the DFS on.
See CLRS p. 541.
enter_vertex, when present, is called just before visiting a vertex
for the first time (and only once) with the vertex id as a parameter.
leave_vertex, when present, is called just after visiting a vertex
for the first time (and only once) with the vertex id as a parameter.
"""
if not vertex_set:
vertex_set = self.vertices
# Straight CLRS p.541
discovery = {} # d in CLRS
parents = {} # \pi in CLRS
finish = {} # f in CLRS
t = [0]
(enter, leave, back, other) = xrange(4)
# inspired by http://www.ics.uci.edu/~eppstein/PADS/DFS.py
def handle(v, w, edgetype):
t[0] += 1
if edgetype == enter:
discovery[v] = t[0]
if enter_vertex:
enter_vertex(w)
if v != w:
parents[w] = v
elif edgetype == leave:
finish[w] = t[0]
if leave_vertex:
leave_vertex(w)
elif edgetype == back and raise_if_cyclic:
raise GraphContainsCycles(v, w)
visited = set()
gray = set()
# helper function to build stack structure
def st(v): return (v, iter(self.adjacency_list[v]))
for vertex in vertex_set:
if vertex not in visited:
handle(vertex, vertex, enter)
visited.add(vertex)
stack = Stack()
stack.push(st(vertex))
gray.add(vertex)
while stack.size:
parent, children = stack.top()
try:
child, _ = children.next()
if child in visited:
handle(parent, child, (child in gray
and back
or other))
else:
handle(parent, child, enter)
visited.add(child)
stack.push(st(child))
gray.add(child)
except StopIteration:
gray.remove(parent)
stack.pop()
if stack.size:
handle(stack.top()[0], parent, leave)
handle(vertex, vertex, leave)
return discovery, parents, finish
def dfs(self,
vertex_set=None,
raise_if_cyclic=False,
enter_vertex=None,
leave_vertex=None):
""" dfs(self,vertex_set=None,raise_if_cyclic=False,enter_vertex=None,
leave_vertex=None) -> (discovery, parent, finish)
Performs a depth-first search on a graph and returns three dictionaries with
relevant information. If vertex_set is not None, then it is used as
the list of ids to perform the DFS on.
See CLRS p. 541.
enter_vertex, when present, is called just before visiting a vertex
for the first time (and only once) with the vertex id as a parameter.
leave_vertex, when present, is called just after visiting a vertex
for the first time (and only once) with the vertex id as a parameter.
"""
if not vertex_set:
vertex_set = self.vertices
# Ugly ugly python
# http://mail.python.org/pipermail/python-list/2006-April/378964.html
# We cannot explicitly "del data":
# http://www.python.org/dev/peps/pep-0227/
class Closure(object):
def clear(self):
del self.discovery
del self.parent
del self.finish
del self.t
# Straight CLRS p.541
data = Closure()
data.discovery = {} # d in CLRS
data.parent = {} # \pi in CLRS
data.finish = {} # f in CLRS
data.t = 0
(enter, leave, back, other) = xrange(4)
# inspired by http://www.ics.uci.edu/~eppstein/PADS/DFS.py
def handle(v, w, edgetype):
data.t += 1
if edgetype == enter:
data.discovery[v] = data.t
if enter_vertex:
enter_vertex(w)
if v != w:
data.parent[w] = v
elif edgetype == leave:
data.finish[w] = data.t
if leave_vertex:
leave_vertex(w)
elif edgetype == back and raise_if_cyclic:
raise self.GraphContainsCycles(v, w)
visited = set()
gray = set()
# helper function to build stack structure
def st(v):
return (v, iter(self.adjacency_list[v]))
for vertex in vertex_set:
if vertex not in visited:
handle(vertex, vertex, enter)
visited.add(vertex)
stack = Stack()
stack.push(st(vertex))
gray.add(vertex)
while stack.size:
parent, children = stack.top()
try:
child, _ = children.next()
if child in visited:
handle(parent, child,
(child in gray and back or other))
else:
handle(parent, child, enter)
visited.add(child)
stack.push(st(child))
gray.add(child)
except StopIteration:
gray.remove(parent)
stack.pop()
if stack.size:
handle(stack.top()[0], parent, leave)
handle(vertex, vertex, leave)
result = (data.discovery, data.parent, data.finish)
data.clear()
return result
def dfs(self,
vertex_set=None,
raise_if_cyclic=False,
enter_vertex=None,
leave_vertex=None):
""" dfs(self,vertex_set=None,raise_if_cyclic=False,enter_vertex=None,
leave_vertex=None) -> (discovery, parent, finish)
Performs a depth-first search on a graph and returns three dictionaries with
relevant information. If vertex_set is not None, then it is used as
the list of ids to perform the DFS on.
See CLRS p. 541.
enter_vertex, when present, is called just before visiting a vertex
for the first time (and only once) with the vertex id as a parameter.
leave_vertex, when present, is called just after visiting a vertex
for the first time (and only once) with the vertex id as a parameter.
"""
if not vertex_set:
vertex_set = self.vertices
# Straight CLRS p.541
discovery = {} # d in CLRS
parents = {} # \pi in CLRS
finish = {} # f in CLRS
t = [0]
(enter, leave, back, other) = xrange(4)
# inspired by http://www.ics.uci.edu/~eppstein/PADS/DFS.py
def handle(v, w, edgetype):
t[0] += 1
if edgetype == enter:
discovery[v] = t[0]
if enter_vertex:
enter_vertex(w)
if v != w:
parents[w] = v
elif edgetype == leave:
finish[w] = t[0]
if leave_vertex:
leave_vertex(w)
elif edgetype == back and raise_if_cyclic:
raise GraphContainsCycles(v, w)
visited = set()
gray = set()
# helper function to build stack structure
def st(v):
return (v, iter(self.adjacency_list[v]))
for vertex in vertex_set:
if vertex not in visited:
handle(vertex, vertex, enter)
visited.add(vertex)
stack = Stack()
stack.push(st(vertex))
gray.add(vertex)
while stack.size:
parent, children = stack.top()
try:
child, _ = children.next()
if child in visited:
handle(parent, child,
(child in gray and back or other))
else:
handle(parent, child, enter)
visited.add(child)
stack.push(st(child))
gray.add(child)
except StopIteration:
gray.remove(parent)
stack.pop()
if stack.size:
handle(stack.top()[0], parent, leave)
handle(vertex, vertex, leave)
return discovery, parents, finish