Python PriorityQueue.buildHeap方法代碼示例

# 需要導入模塊: from priorityQueue import PriorityQueue [as 別名]
# 或者: from priorityQueue.PriorityQueue import buildHeap [as 別名]
def prim(aGraph, startVertex):
    # create a priority queue that uses distance as the value to determine priority and thus its position
    # use the distance to the vertex as the priority because while exploring the next vertex, want to explore the vertex that has the smallest distance
    # decreaseKey method used when the distance to a vertex that is already in the queue is reduced, and thus moves that vertex toward the front of the queue.
    pQueue = PriorityQueue()
    # initialize the state of the graph 
    for vertex in aGraph:
        # initialally all vertices values are = infinity (sys.maxint) because we assume the greatest value and then update appropiately
        vertex.setDistance(sys.maxsize)
        vertex.setPred(None)
    
    # distance represents distance from the startVertex, trivially 0 for the startVertex
    startVertex.setDistance(0)
    # key value pair
    # key is distance and vertex is the value
    pQueue.buildHeap([ (vertex.getDistance(), vertex) for vertex in aGraph ])
    
    while not pQueue.isEmpty():
        currentVertex = pQueue.delMin()
        # iterate over the currentVertex's edges
        for nextVertex in currentVertex.getConnections():
            # calculate the weight from currentVertex to nextVertex
            newCost = currentVertex.getWeight(nextVertex)
            
            # found a shorter path
            # node is not considered to be part of the spanning tree until it is removed from the priority queue.
            # nextVertex in pQueue means that vertex is not yet in the spanning tree so it is safe to add (ensures an acyclic graph)
            if nextVertex in pQueue and newCost< nextVertex.getDistance():
                # assign the predecessor appropiately
                nextVertex.setPred(currentVertex)
                # set a new distance on the nextVertex
                nextVertex.setDistance(newCost)
                # update the priorityQueue with the correct values
                pQueue.decreaseKey(nextVertex, newCost)

# 需要導入模塊: from priorityQueue import PriorityQueue [as 別名]
# 或者: from priorityQueue.PriorityQueue import buildHeap [as 別名]
def dijkstra(aGraph, startVertex):
    # create a priority queue that uses distance as the value to determine priority and thus its position
    # use the distance to the vertex as the priority because while exploring the next vertex, want to explore the vertex that has the smallest distance
    # decreaseKey method used when the distance to a vertex that is already in the queue is reduced, and thus moves that vertex toward the front of the queue.
    pQueue = PriorityQueue()
    
    # distance represents distance from the startVertex, trivially 0 for the startVertex
    # initialally all vertices values are = infinity (sys.maxint) because we assume the greatest value and then update appropiately
    startVertex.setDistance(0)
    
    # key value pair
    # key is distance and vertex is the value
    pQueue.buildHeap([ (vertex.getDistance(), vertex) for vertex in aGraph ])
    
    while not pQueue.isEmpty():
        currentVertex = pQueue.delMin()
        # iterate over the currentVertex's edges
        for nextVertex in currentVertex.getConnections():
            # distance of current vertex and the weight of it's edges
            newDistance = currentVertex.getDistance() + currentVertex.getWeight(nextVertex)
            # found a shorter path
            if newDistance < nextVertex.getDistance():
                # set a new distance on the nextVertex
                nextVertex.setDistance(newDistance)
                # assign the predecessor appropiately
                nextVertex.setPred(currentVertex)
                # update the priorityQueue with the correct values
                pQueue.decreaseKey(nextVertex, newDistance)

# 需要導入模塊: from priorityQueue import PriorityQueue [as 別名]
# 或者: from priorityQueue.PriorityQueue import buildHeap [as 別名]
def Dijkstras(graph,start):   
	pq=PriorityQueue()
	start.setDistance(0)
	pq.buildHeap([(v.getDistance(),v) for v in graph])   # distance is the key in the priority queue
	while not pq.isEmpty():
		currentvertex=pq.delMin()
		for newvertex in currentvertex.getConnections():
			newDist=currentvertex.getDistance()+currentvertex.getWeight(newvertex)
			if newDist<newvertex.getDistance(): 
				# at the start the distance of all the vertices is set to maximum. That's why the if statement will be executed
				newvertex.setDistance(newDist)
				newvertex.setPredecessor(currentvertex)
				pq.decreaseKey(newvertex,newDist)

# 需要導入模塊: from priorityQueue import PriorityQueue [as 別名]
# 或者: from priorityQueue.PriorityQueue import buildHeap [as 別名]
def prim(graph,start):     # it belongs to the family of greedy algorithms
	pq=PriorityQueue()
	for v in graph:
		v.setDistance(sys.maxsize)
		v.setPredecessor(None)
	start.setDistance(0)
	pq.buildHeap([(v.getDistance(),v) for v in graph])
	while not pq.isEmpty()
		currentvertex=pq.delMin()
		for newvertex in currentvertex.getConnections():
			newDist=currentvertex.getWeight(newvertex)
			if newDist<newvertex.getDistance() and newvertex in pq:
				newvertex.setDistance(newDist)
				newvertex.setPredecessor(currentvertex)
				pq.decreaseKey(newvertex,newDist)