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