pgm16_18.txt

Data Structures And Algorithms With Object-Oriented Design Patterns In Python (2003) source code and

#
# This file contains the Python code from Program 16.18 of
# "Data Structures and Algorithms
# with Object-Oriented Design Patterns in Python"
# by Bruno R. Preiss.
#
# Copyright (c) 2003 by Bruno R. Preiss, P.Eng.  All rights reserved.
#
# http://www.brpreiss.com/books/opus7/programs/pgm16_18.txt
#
class Algorithms(object):

    def PrimsAlgorithm(g, s):
        n = g.numberOfVertices
        table = Array(n)
        for v in xrange(n):
            table[v] = Algorithms.Entry()
        table[s].distance = 0
        queue = BinaryHeap(g.numberOfEdges)
        queue.enqueue(Association(0, g[s]))
        while not queue.isEmpty:
            assoc = queue.dequeueMin()
            v0 = assoc.value
            if not table[v0.number].known:
                table[v0.number].known = True
                for e in v0.emanatingEdges:
                    v1 = e.mateOf(v0)
                    d = e.weight
                    if not table[v1.number].known and \
                            table[v1.number].distance > d:
                        table[v1.number].distance = d
                        table[v1.number].predecessor = v0.number
                        queue.enqueue(Association(d, v1))
        result = GraphAsLists(n)
        for v in xrange(n):
            result.addVertex(v)
        for v in xrange(n):
            if v != s:
                result.addEdge(v, table[v].predecessor)
        return result
    PrimsAlgorithm = staticmethod(PrimsAlgorithm)