python计算最大优先级队列实例

代码如下:
# -*- coding: utf-8 -*-

class Heap(object):

    @classmethod
    def parent(cls, i):
        """父结点下标"""
        return int((i - 1) >> 1);

    @classmethod
    def left(cls, i):
        """左儿子下标"""
        return (i << 1) + 1;

    @classmethod
    def right(cls, i):
        """右儿子下标"""
        return (i << 1) + 2;

class MaxPriorityQueue(list, Heap):

    @classmethod
    def max_heapify(cls, A, i, heap_size):
        """最大堆化A[i]为根的子树"""
        l, r = cls.left(i), cls.right(i)
        if l < heap_size and A[l] > A[i]:
            largest = l
        else:
            largest = i
        if r < heap_size and A[r] > A[largest]:
            largest = r
        if largest != i:
            A[i], A[largest] = A[largest], A[i]
            cls.max_heapify(A, largest, heap_size)

    def maximum(self):
        """返回最大元素，伪码如下：
        HEAP-MAXIMUM(S)
        1  return A[1]

        T(n) = O(1)
        """
        return self[0]

    def extract_max(self):
        """去除并返回最大元素，伪码如下：
        HEAP-EXTRACT-MAX(A)
        1  if heap-size[A] < 1
        2    then error "heap underflow"
        3  max ← A[1]
        4  A[1] ← A[heap-size[A]] // 尾元素放到第一位
        5  heap-size[A] ← heap-size[A] - 1 // 减小heap-size[A]
        6  MAX-HEAPIFY(A, 1) // 保持最大堆性质
        7  return max

        T(n) = θ(lgn)