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69 lines
2.0 KiB
Python
69 lines
2.0 KiB
Python
5 years ago
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class DirectedGraph(object):
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"""A graph structure with directed edges.
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"""
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def __init__(self):
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self._vertices = set()
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self._forwards = {} # <key> -> Set[<key>]
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self._backwards = {} # <key> -> Set[<key>]
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def __iter__(self):
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return iter(self._vertices)
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def __len__(self):
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return len(self._vertices)
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def __contains__(self, key):
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return key in self._vertices
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def copy(self):
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"""Return a shallow copy of this graph.
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"""
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other = DirectedGraph()
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other._vertices = set(self._vertices)
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other._forwards = {k: set(v) for k, v in self._forwards.items()}
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other._backwards = {k: set(v) for k, v in self._backwards.items()}
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return other
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def add(self, key):
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"""Add a new vertex to the graph.
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"""
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if key in self._vertices:
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raise ValueError("vertex exists")
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self._vertices.add(key)
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self._forwards[key] = set()
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self._backwards[key] = set()
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def remove(self, key):
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"""Remove a vertex from the graph, disconnecting all edges from/to it.
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"""
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self._vertices.remove(key)
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for f in self._forwards.pop(key):
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self._backwards[f].remove(key)
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for t in self._backwards.pop(key):
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self._forwards[t].remove(key)
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def connected(self, f, t):
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return f in self._backwards[t] and t in self._forwards[f]
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def connect(self, f, t):
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"""Connect two existing vertices.
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Nothing happens if the vertices are already connected.
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"""
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if t not in self._vertices:
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raise KeyError(t)
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self._forwards[f].add(t)
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self._backwards[t].add(f)
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def iter_edges(self):
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for f, children in self._forwards.items():
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for t in children:
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yield f, t
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def iter_children(self, key):
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return iter(self._forwards[key])
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def iter_parents(self, key):
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return iter(self._backwards[key])
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