python实现最大优先队列

#! /usr/bin/env python#coding=utf-8class Heap(object): #求给定下标i的父节点下标 def Parent(self, i):  if i%2==0:   return i/2 - 1  else:   return i/2 #求给定下标i的左孩子下标 def Left(self, i):  return 2*i+1 #求给定下标i的右孩子下标 def Right(self, i):  return 2*i+2 #维护堆的性质：遵循最大堆 def MaxHeapify(self, a, i, heap_size):  l=self.Left(i)  r=self.Right(i)  largest = i  if l<heap_size and a[l]>a[largest]:#下标从0~heap_size-1   largest=l  if r<heap_size and a[r]>a[largest]:   largest=r  if largest!=i:#若当前节点不是最大的，下移   a[i], a[largest] = a[largest], a[i]#交换a[i]和a[largest]   self.MaxHeapify(a, largest, heap_size)#追踪下移的节点 #建堆  def BuildMaxHeap(self, a):  heap_size=len(a)  for i in range(heap_size/2 - 1, -1, -1):#从最后一个非叶节点开始调整   #a[heap_size/2 - 1]~a[0]都是非叶节点，其他的是叶子节点   self.MaxHeapify(a, i, heap_size) #堆排序算法  def HeapSort(self, a):  heap_size=len(a)  '''step1:初始化堆，将a[0...n-1]构造为堆（堆顶a[0]为最大元素）'''  self.BuildMaxHeap(a)  for i in range(len(a)-1, 0, -1):   #print a   '''step2:将当前无序区的堆顶元素a[0]与该区间最后一个记录交换    得到新的无序区a[0...n-2]和新的有序区a[n-1],有序区的范围从    后往前不断扩大，直到有n个'''   a[0], a[i] = a[i], a[0]#每次将剩余元素中的最大者放到最后面a[i]处    heap_size -= 1   '''step3:为避免交换后新的堆顶违反堆的性质，因此将新的无序区调整为新    的堆'''   self.MaxHeapify(a, 0, heap_size)#最大优先队列的实现class PriorityQ(Heap): #返回具有最大键字的元素 def HeapMaximum(self, a):  return a[0] #去掉并返回具有最大键字的元素 def HeapExtractMax(self, a):  heap_size=len(a)  #if heap_size<0:  # error "heap underflow"  if heap_size>0:   max=a[0]   a[0]=a[heap_size-1]   #heap_size -= 1 #该处不对，并没有真正实现数组长度减一   del a[heap_size-1]#!!!!!!   self.MaxHeapify(a, 0, len(a))   return max #将a[i]处的关键字增加到key def HeapIncreaseKey(self, a, i, key):  if key<a[i]:   print "new key is smaller than current one"  else:   a[i]=key   '''当前元素不断与其父节点进行比较，如果当前元素关键字较大，则与其    父节点进行交换。不断重复此过程'''   while i>0 and a[self.Parent(i)]<a[i]:    a[i], a[self.Parent(i)] = a[self.Parent(i)], a[i]    i=self.Parent(i)  #增加元素 def MaxHeapInsert(self, a, key):  #heap_size=len(a)  #heap_size += 1  #a[heap_size-1]=-65535  a.append(-65535)#在a的末尾增加一个关键字为负无穷的叶节点扩展最大堆  heap_size=len(a)  self.HeapIncreaseKey(a, heap_size-1, key)if __name__ == '__main__': H = Heap() P = PriorityQ() x = [0, 2, 6, 98, 34, -5, 23, 11, 89, 100, 4] #x1= [3,9,8,4,5,2,10,18] #H.HeapSort(x) #H.HeapSort(x1) #print x #print x1 H.BuildMaxHeap(x)#首先建立大顶堆 print '%s %r' % ('BigHeap1:', x) # %r是万能输出格式 print '%s %d' % ('Maximun:', P.HeapMaximum(x)) print '%s %d' % ('ExtractMax:', P.HeapExtractMax(x)) print '%s %r' % ('BigHeap2:', x) #P.MaxHeapInsert(x, 100) #print x P.HeapIncreaseKey(x, 2, 20) print x P.HeapIncreaseKey(x, 2, 30) print x P.MaxHeapInsert(x, 100) print x

BigHeap1: [100, 98, 23, 89, 34, -5, 6, 11, 0, 2, 4] Maximun: 100 ExtractMax: 100 BigHeap2: [98, 89, 23, 11, 34, -5, 6, 4, 0, 2] new key is smaller than current one [98, 89, 23, 11, 34, -5, 6, 4, 0, 2] [98, 89, 30, 11, 34, -5, 6, 4, 0, 2] [100, 98, 30, 11, 89, -5, 6, 4, 0, 2, 34]