mirror of
https://github.com/MartinThoma/LaTeX-examples.git
synced 2025-04-26 06:48:04 +02:00
94 lines
2.6 KiB
Python
94 lines
2.6 KiB
Python
|
def strongly_connected_components(graph):
|
||
|
|
"""
|
||
|
|
Tarjan's Algorithm (named for its discoverer, Robert Tarjan) is a
|
||
|
|
graph theory algorithm for finding the strongly connected
|
||
|
|
components of a graph.
|
||
|
|
|
||
|
|
Based on: http://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm
|
||
|
|
@author: Dries Verdegem, some minor edits by Martin Thoma
|
||
|
|
@source: http://www.logarithmic.net/pfh/blog/01208083168
|
||
|
|
"""
|
||
|
|
|
||
|
|
index_counter = 0
|
||
|
|
stack = []
|
||
|
|
lowlinks = {}
|
||
|
|
index = {}
|
||
|
|
result = []
|
||
|
|
|
||
|
|
def strongconnect(node, index_counter):
|
||
|
|
print("Start with node: %s###########################" % node)
|
||
|
|
# set the depth index for this node to the smallest unused index
|
||
|
|
print("lowlinks:\t%s" % lowlinks)
|
||
|
|
print("index:\t%s" % index)
|
||
|
|
print("stack:\t%s" % stack)
|
||
|
|
|
||
|
|
index[node] = index_counter
|
||
|
|
lowlinks[node] = index_counter
|
||
|
|
index_counter += 1
|
||
|
|
stack.append(node)
|
||
|
|
|
||
|
|
# Consider successors of `node`
|
||
|
|
try:
|
||
|
|
successors = graph[node]
|
||
|
|
except:
|
||
|
|
successors = []
|
||
|
|
|
||
|
|
# Depth first search
|
||
|
|
for successor in successors:
|
||
|
|
# Does the current node point to a node that was already
|
||
|
|
# visited?
|
||
|
|
if successor not in lowlinks:
|
||
|
|
print("successor not in lowlinks: %s -> %s (node, successor)" % (node, successor))
|
||
|
|
# Successor has not yet been visited; recurse on it
|
||
|
|
strongconnect(successor, index_counter)
|
||
|
|
lowlinks[node] = min(lowlinks[node],lowlinks[successor])
|
||
|
|
elif successor in stack:
|
||
|
|
#else:
|
||
|
|
print("successor in stack: %s -> %s" % (node, successor));
|
||
|
|
# the successor is in the stack and hence in the
|
||
|
|
# current strongly connected component (SCC)
|
||
|
|
lowlinks[node] = min(lowlinks[node],index[successor])
|
||
|
|
else:
|
||
|
|
print("This happens sometimes. node: %s, successor: %s" % (node, successor))
|
||
|
|
print("Lowlinks: %s" %lowlinks)
|
||
|
|
print("stack: %s" % stack)
|
||
|
|
|
||
|
|
# If `node` is a root node, pop the stack and generate an SCC
|
||
|
|
if lowlinks[node] == index[node]:
|
||
|
|
print("Got root node: %s (index/lowlink: %i)" % (node, lowlinks[node]))
|
||
|
|
connected_component = []
|
||
|
|
|
||
|
|
while True:
|
||
|
|
successor = stack.pop()
|
||
|
|
print("pop: %s" % successor)
|
||
|
|
connected_component.append(successor)
|
||
|
|
if successor == node: break
|
||
|
|
|
||
|
|
component = tuple(connected_component)
|
||
|
|
|
||
|
|
# storing the result
|
||
|
|
result.append(component)
|
||
|
|
else:
|
||
|
|
print("Node: %s, lowlink: %i, index: %i" % (node, lowlinks[node], index[node]))
|
||
|
|
|
||
|
|
for node in graph:
|
||
|
|
if node not in lowlinks:
|
||
|
|
strongconnect(node, index_counter)
|
||
|
|
|
||
|
|
return result
|
||
|
|
|
||
|
|
graph = {'a': ['b'],
|
||
|
|
'b': ['c'],
|
||
|
|
'c': ['d', 'e'],
|
||
|
|
'd': ['a', 'e', 'h'],
|
||
|
|
'e': ['c', 'f'],
|
||
|
|
'f': ['g', 'i'],
|
||
|
|
'g': ['h', 'f'],
|
||
|
|
'h': ['j'],
|
||
|
|
'i': ['g', 'f'],
|
||
|
|
'j': ['i'],
|
||
|
|
'k': [],
|
||
|
|
'h': []}
|
||
|
|
|
||
|
|
print strongly_connected_components(graph)
|