Discussion :

[momo199]

Bonjour, je dois donner l'arbre recouvrant minimum de G et donc j'ai utilisé l'algo de prim. Mais j'arrive pas à ajouter les valeurs correspondant aux sommets voisins de G

Code :

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G= {
'a':{ 'b':1.54 , 'c':2.97} ,
'b':{ 'a':1.54 , 'f':5 , 'c':10.5} ,
'c':{ 'a':2.97 , 'b':10.5 , 'f':2.33 , 'e':4.25} ,
'd':{ 'f':8.01,'e':3.73 } ,
'e':{ 'c':4.25 , 'd':3.73} ,
'f':{ 'b':5 , 'c':2.33 , 'd':8.01}
}
 
def graphprim(G):
F=priority_dict()
for u in G:F[u]=float('inf')
s=premiersommet(G)
F[s]=0
pere[s]=None
V=dict()
vu=set()
while F:
u=F.pop_smallest()
vu.add(u)
for vin G[u]:
if v not in vu:
if v in F and G[u][v]<F[v]:
F[v]=G[u][v] #poids de chaque sommet voisin
for n in F:
V[u]=dict({v:F[v]}) #dictionnaire à returner
for key,value in V.items():
if pere[value]==key and F[value] != float('inf'):
V[key][value]=F[value] #ajout de chaque sommet voisin de key existant 
F.pop_smallest()
 
return V

[Sve@r]

Bonjour

Ton code ressemble à du Python mais ce n'en est pas. En tout cas pas du Python exécutable. En tout état de cause, il plante à la ligne 12. Probablement parce qu'il manque des éléments essentiels à sa syntaxe. Et ce n'est pas à cause du priority_dict. Tu aurais écrit F="toto" ça aurait été pareil.

[momo199]

priority_dict est un module qui n'existe pas dans python. Donc voici le code du module:

Code :

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# http://code.activestate.com/recipes/522995/
# https://gist.github.com/matteodellamico/4451520
# http://code.activestate.com/recipes/522995-priority-dict-a-priority-queue-with-updatable-prio/
 
# This is free and unencumbered software released into the public domain.
#
# Anyone is free to copy, modify, publish, use, compile, sell, or
# distribute this software, either in source code form or as a compiled
# binary, for any purpose, commercial or non-commercial, and by any
# means.
#
# In jurisdictions that recognize copyright laws, the author or authors
# of this software dedicate any and all copyright interest in the
# software to the public domain. We make this dedication for the benefit
# of the public at large and to the detriment of our heirs and
# successors. We intend this dedication to be an overt act of
# relinquishment in perpetuity of all present and future rights to this
# software under copyright law.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
# OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
# ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
# OTHER DEALINGS IN THE SOFTWARE.
#
# For more information, please refer to <http://unlicense.org/>
 
# By Matteo Dell'Amico
 
from heapq import heapify, heappush, heappop
 
class priority_dict(dict):
    """Dictionary that can be used as a priority queue.
 
    Keys of the dictionary are items to be put into the queue, and values
    are their respective priorities. All dictionary methods work as expected.
    The advantage over a standard heapq-based priority queue is
    that priorities of items can be efficiently updated (amortized O(1))
    using code as 'thedict[item] = new_priority.'
 
    The 'smallest' method can be used to return the object with lowest
    priority, and 'pop_smallest' also removes it.
 
    The 'sorted_iter' method provides a destructive sorted iterator.
    """
 
    def __init__(self, *args, **kwargs):
        super(priority_dict, self).__init__(*args, **kwargs)
        self._rebuild_heap()
 
    def _rebuild_heap(self):
        self._heap = [(v, k) for k, v in self.items()]
        heapify(self._heap)
 
    def smallest(self):
        """Return the item with the lowest priority.
 
        Raises IndexError if the object is empty.
        """
 
        heap = self._heap
        v, k = heap[0]
        while k not in self or self[k] != v:
            heappop(heap)
            v, k = heap[0]
        return k
 
    def pop_smallest(self):
        """Return the item with the lowest priority and remove it.
 
        Raises IndexError if the object is empty.
        """
 
        heap = self._heap
        v, k = heappop(heap)
        while k not in self or self[k] != v:
            v, k = heappop(heap)
        del self[k]
        return k
 
    def __setitem__(self, key, val):
        # We are not going to remove the previous value from the heap,
        # since this would have a cost O(n).
 
        super(priority_dict, self).__setitem__(key, val)
 
        if len(self._heap) < 2 * len(self):
            heappush(self._heap, (val, key))
        else:
            # When the heap grows larger than 2 * len(self), we rebuild it
            # from scratch to avoid wasting too much memory.
            self._rebuild_heap()
 
    def setdefault(self, key, val):
        if key not in self:
            self[key] = val
            return val
        return self[key]
 
    def update(self, *args, **kwargs):
        # Reimplementing dict.update is tricky -- see e.g.
        # http://mail.python.org/pipermail/python-ideas/2007-May/000744.html
        # We just rebuild the heap from scratch after passing to super.
 
        super(priority_dict, self).update(*args, **kwargs)
        self._rebuild_heap()
 
    def sorted_iter(self):
        """Sorted iterator of the priority dictionary items.
 
        Beware: this will destroy elements as they are returned.
        """
 
        while self:
            yield self.pop_smallest()

[Sve@r]

Et ce n'est pas à cause du priority_dict. Tu aurais écrit F="toto" ça aurait été pareil.

priority_dict est un module qui n'existe pas dans python. Donc voici le code du module:

Quel mot tu ne comprends pas dans "ce n'est pas à cause du priority_dict" ???

[lizliz1999]

Bonjour, je dois donner l'arbre recouvrant minimum de G et donc j'ai utilisé l'algo de prim. Mais j'arrive pas à ajouter les valeurs correspondant aux sommets voisins de G

Code :

Sélectionner tout - Visualiser dans une fenêtre à part

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G= {
'a':{ 'b':1.54 , 'c':2.97} ,
'b':{ 'a':1.54 , 'f':5 , 'c':10.5} ,
'c':{ 'a':2.97 , 'b':10.5 , 'f':2.33 , 'e':4.25} ,
'd':{ 'f':8.01,'e':3.73 } ,
'e':{ 'c':4.25 , 'd':3.73} ,
'f':{ 'b':5 , 'c':2.33 , 'd':8.01}
}
 
def graphprim(G):
F=priority_dict()
for u in G:F[u]=float('inf')
s=premiersommet(G)
F[s]=0
pere[s]=None
V=dict()
vu=set()
while F:
u=F.pop_smallest()
vu.add(u)
for vin G[u]:
if v not in vu:
if v in F and G[u][v]<F[v]:
F[v]=G[u][v] #poids de chaque sommet voisin
for n in F:
V[u]=dict({v:F[v]}) #dictionnaire à returner
for key,value in V.items():
if pere[value]==key and F[value] != float('inf'):
V[key][value]=F[value] #ajout de chaque sommet voisin de key existant 
F.pop_smallest()
 
return V