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from abc import ABCMeta, abstractmethod |
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from pyalgs.algorithms.commons import util |
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from pyalgs.algorithms.graphs.topological_sort import DepthFirstOrder |
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from pyalgs.data_structures.commons.priority_queue import IndexMinPQ |
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from pyalgs.data_structures.commons.stack import Stack |
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from pyalgs.data_structures.graphs.graph import Digraph, Graph, EdgeWeightedGraph |
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class ShortestPath(object): |
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__metaclass__ = ABCMeta |
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@abstractmethod |
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def shortestPathTo(self, v): |
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pass |
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@abstractmethod |
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def hasPathTo(self, v): |
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pass |
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@abstractmethod |
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def path_length_to(self, v): |
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pass |
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class DijkstraShortestPath(ShortestPath): |
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edgeTo = None |
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s = 0 |
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pq = None |
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cost = None |
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def __init__(self, G, s): |
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if isinstance(G, Graph): |
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raise ValueError('Graph must be edge weighted') |
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if isinstance(G, Digraph): |
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raise ValueError('Graph must be edge weighted') |
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if isinstance(G, EdgeWeightedGraph): |
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G = G.to_edge_weighted_digraph() |
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vertex_count = G.vertex_count() |
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self.pq = IndexMinPQ(vertex_count) |
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self.s = s |
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self.marked = [False] * vertex_count |
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self.edgeTo = [None] * vertex_count |
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self.cost = [float("inf")] * vertex_count |
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self.cost[s] = 0 |
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self.pq.insert(s, 0.0) |
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while not self.pq.is_empty(): |
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v = self.pq.del_min() |
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self.marked[v] = True |
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for e in G.adj(v): |
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self.relax(e) |
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def relax(self, e): |
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v = e.start() |
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w = e.end() |
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if self.cost[w] > self.cost[v] + e.weight: |
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self.cost[w] = self.cost[v] + e.weight |
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self.edgeTo[w] = e |
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if self.pq.contains_index(w): |
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self.pq.decrease_key(w, self.cost[w]) |
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else: |
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self.pq.insert(w, self.cost[w]) |
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def hasPathTo(self, v): |
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return self.marked[v] |
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def shortestPathTo(self, v): |
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path = Stack.create() |
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x = v |
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while x != self.s: |
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path.push(self.edgeTo[x]) |
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x = self.edgeTo[x].start() |
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return path.iterate() |
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def path_length_to(self, v): |
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return self.cost[v] |
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85
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class TopologicalSortShortestPath(ShortestPath): |
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marked = None |
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edgeTo = None |
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cost = None |
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s = 0 |
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def __init__(self, G, s): |
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vertex_count = G.vertex_count() |
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self.marked = [False] * vertex_count |
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self.edgeTo = [None] * vertex_count |
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self.cost = [float('inf')] * vertex_count |
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self.s = s |
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dfo = DepthFirstOrder(G) |
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orders = dfo.postOrder() |
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self.cost[s] = 0 |
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for v in orders: |
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for e in G.adj(v): |
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self.relax(e) |
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108
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def relax(self, e): |
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v = e.start() |
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w = e.end() |
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if self.cost[w] > self.cost[v] + e.weight: |
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self.cost[w] = self.cost[v] + e.weight |
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self.edgeTo[w] = e |
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self.marked[w] = True |
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def shortestPathTo(self, v): |
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path = Stack.create() |
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x = v |
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while x != self.s: |
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path.push(self.edgeTo[x]) |
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x = self.edgeTo[x].start() |
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return path.iterate() |
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125
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def hasPathTo(self, v): |
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return self.marked[v] |
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128
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def path_length_to(self, v): |
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return self.cost[v] |
chen0040 /
pyalgs
