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from abc import ABCMeta, abstractmethod |
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from pyalgs.algorithms.commons.union_find import UnionFind |
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from pyalgs.algorithms.commons.util import less |
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from pyalgs.data_structures.commons.bag import Bag |
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from pyalgs.data_structures.commons.priority_queue import MinPQ, IndexMinPQ |
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from pyalgs.data_structures.graphs.graph import EdgeWeightedGraph |
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class MST(object): |
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__metaclass__ = ABCMeta |
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@abstractmethod |
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def spanning_tree(self): |
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pass |
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class KruskalMST(MST): |
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tree = None |
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def __init__(self, G): |
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if not isinstance(G, EdgeWeightedGraph): |
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raise ValueError('Graph must be edge weighted and undirected to run MST') |
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minpq = MinPQ.create() |
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self.tree = Bag() |
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for e in G.edges(): |
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minpq.enqueue(e) |
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uf = UnionFind.create(G.vertex_count()) |
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while not minpq.is_empty() and self.tree.size() < G.vertex_count() - 1: |
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e = minpq.del_min() |
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v = e.either() |
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w = e.other(v) |
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if not uf.connected(v, w): |
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uf.union(v, w) |
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self.tree.add(e) |
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def spanning_tree(self): |
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return self.tree.iterate() |
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class LazyPrimMST(MST): |
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tree = None |
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marked = None |
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minpq = None |
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def __init__(self, G): |
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if not isinstance(G, EdgeWeightedGraph): |
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raise ValueError('Graph must be edge weighted and undirected to run MST') |
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self.minpq = MinPQ.create() |
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self.tree = Bag() |
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vertex_count = G.vertex_count() |
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self.marked = [False] * vertex_count |
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self.visit(G, 0) |
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while not self.minpq.is_empty() and self.tree.size() < vertex_count - 1: |
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edge = self.minpq.del_min() |
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v = edge.either() |
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w = edge.other(v) |
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if self.marked[v] and self.marked[w]: |
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continue |
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self.tree.add(edge) |
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if not self.marked[v]: |
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self.visit(G, v) |
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if not self.marked[w]: |
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self.visit(G, w) |
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def visit(self, G, v): |
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self.marked[v] = True |
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for e in G.adj(v): |
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w = e.other(v) |
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if not self.marked[w]: |
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self.minpq.enqueue(e) |
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def spanning_tree(self): |
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return self.tree.iterate() |
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class EagerPrimMST(MST): |
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path = None |
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pq = None |
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marked = None |
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def __init__(self, G): |
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if not isinstance(G, EdgeWeightedGraph): |
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raise ValueError('Graph must be edge weighted and undirected to run MST') |
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vertex_count = G.vertex_count() |
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self.pq = IndexMinPQ(vertex_count) |
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self.path = Bag() |
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self.marked = [False] * vertex_count |
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self.visit(G, 0) |
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while not self.pq.is_empty() and self.path.size() < vertex_count - 1: |
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e = self.pq.min_key() |
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w = self.pq.del_min() |
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self.path.add(e) |
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if not self.marked[w]: |
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self.visit(G, w) |
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def visit(self, G, v): |
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self.marked[v] = True |
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for e in G.adj(v): |
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w = e.other(v) |
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if not self.marked[w]: |
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if self.pq.contains_index(w): |
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old_e = self.pq.get(w) |
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if less(e, old_e): |
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self.pq.decrease_key(w, e) |
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else: |
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self.pq.insert(w, e) |
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def spanning_tree(self): |
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return self.path.iterate() |
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chen0040 /
pyalgs
