106 lines
3.7 KiB
Python
Executable File
106 lines
3.7 KiB
Python
Executable File
# -*- coding: utf-8 -*-
|
|
|
|
|
|
class SimpleAcyclicOrientedGraph(object):
|
|
"""
|
|
Stores a graph data structure and allows operation with it.
|
|
Example data: {'P1': ['P2'], 'P3': ['P4', 'P5'], 'P2': 'P3'}
|
|
Graph is constructed by adding oriented edges one by one. It can not contain cycles.
|
|
Main result is spanning line, it determines ordering of the nodes.
|
|
"""
|
|
|
|
def __init__(self):
|
|
self._graph = {}
|
|
self._all_nodes = set()
|
|
|
|
def add_edge(self, start, end):
|
|
"""
|
|
Add one edge from node 'start' to node 'end'.
|
|
This operation must not create a cycle in the graph.
|
|
"""
|
|
if start == end:
|
|
raise ValueError(
|
|
"Can not add this kind of edge into graph: %s-%s" % (start, end)
|
|
)
|
|
self._graph.setdefault(start, [])
|
|
if end not in self._graph[start]:
|
|
self._graph[start].append(end)
|
|
self._all_nodes.add(start)
|
|
self._all_nodes.add(end)
|
|
# try to find opposite direction path (from end to start)
|
|
# to detect newly created cycle
|
|
path = SimpleAcyclicOrientedGraph.find_path(self._graph, end, start)
|
|
if path:
|
|
raise ValueError("There is a cycle in the graph: %s" % path)
|
|
|
|
def get_active_nodes(self):
|
|
"""
|
|
nodes connected to any edge
|
|
"""
|
|
active_nodes = set()
|
|
for start, ends in self._graph.items():
|
|
active_nodes.add(start)
|
|
active_nodes.update(ends)
|
|
return active_nodes
|
|
|
|
def is_final_endpoint(self, node):
|
|
"""
|
|
edge(s) ends in this node; no other edge starts in this node
|
|
"""
|
|
if node not in self._all_nodes:
|
|
return ValueError("This node is not found in the graph: %s" % node)
|
|
if node not in self.get_active_nodes():
|
|
return False
|
|
return False if node in self._graph else True
|
|
|
|
def remove_final_endpoint(self, node):
|
|
""""""
|
|
remove_start_points = []
|
|
for start, ends in self._graph.items():
|
|
if node in ends:
|
|
ends.remove(node)
|
|
if not ends:
|
|
remove_start_points.append(start)
|
|
for start in remove_start_points:
|
|
del self._graph[start]
|
|
|
|
@staticmethod
|
|
def find_path(graph, start, end, path=[]):
|
|
"""
|
|
find path among nodes 'start' and 'end' recursively
|
|
"""
|
|
path = path + [start]
|
|
if start == end:
|
|
return path
|
|
if start not in graph:
|
|
return None
|
|
for node in graph[start]:
|
|
if node not in path:
|
|
newpath = SimpleAcyclicOrientedGraph.find_path(graph, node, end, path)
|
|
if newpath:
|
|
return newpath
|
|
return None
|
|
|
|
def prune_graph(self):
|
|
"""
|
|
Construct spanning_line by pruning the graph.
|
|
Looking for endpoints and remove them one by one until graph is empty.
|
|
"""
|
|
spanning_line = []
|
|
while self._graph:
|
|
for node in sorted(self._all_nodes):
|
|
if self.is_final_endpoint(node):
|
|
self.remove_final_endpoint(node)
|
|
spanning_line.insert(0, node)
|
|
# orphan node = no edge is connected with this node
|
|
orphans = self._all_nodes - self.get_active_nodes()
|
|
if orphans:
|
|
# restart iteration not to set size self._all_nodes
|
|
# during iteration
|
|
break
|
|
for orphan in orphans:
|
|
if orphan not in spanning_line:
|
|
spanning_line.insert(0, orphan)
|
|
self._all_nodes.remove(orphan)
|
|
return spanning_line
|