Question

我已经创建了一个堆类，我正在尝试创建一个PriorityQueue类，因此它们可以一起工作。但是，我需要有关代码的Priority Queue部分的帮助。我已经做了一个工作堆。我尝试在互联网上查找帮助，但我不断使用“queue”或“heapq”python实现获得答案。任何人都可以帮助我如何使一个有效的优先级队列课程？我写下了基本的功能名称，但我不知道从那里去哪里。请我坚持一段时间，真的需要一些帮助。这是我的工作堆密码。

class Heap(object):

    def __init__(self, items=None):

        '''Post: A heap is created with specified items.'''

        self.heap = [None]
        if items is None:
            self.heap_size = 0
        else:
            self.heap += items
            self.heap_size = len(items)
            self._build_heap()

    def size(self):

        '''Post: Returns the number of items in the heap.'''

        return self.heap_size

    def _heapify(self, position):

        '''Pre: Items from 0 to position - 1 satisfy the Heap property.
       Post: Heap Property is satisfied for the entire heap.'''

        item = self.heap[position]
        while position * 2 <= self.heap_size:
            child = position * 2
            # If the right child, determine the maximum of two children.
            if (child != self.heap_size and self.heap[child+1] > self.heap[child]):
                child += 1
            if self.heap[child] > item:
                self.heap[position] = self.heap[child]
                position = child
            else:
                break
        self.heap[position] = item

    def delete_max(self):

        '''Pre: Heap property is satisfied
       Post: Maximum element in heap is removed and returned. '''

        if self.heap_size > 0:
            max_item = self.heap[1]
            self.heap[1] = self.heap[self.heap_size]
            self.heap_size -= 1
            self.heap.pop()
            if self.heap_size > 0:
                self._heapify(1)
            return max_item

    def insert(self, item):

        '''Pre: Heap Property is Satisfied.
       Post: Item is inserted in proper location in heap.'''

        self.heap_size += 1
        # extend the length of the list.
        self.heap.append(None)
        position = self.heap_size
        parent = position // 2
        while parent > 0 and self.heap[parent] < item:
            # Move the item down.
            self.heap[position] = self.heap[parent]
            position = parent
            parent = position // 2
        # Puts the new item in the correct spot.
        self.heap[position] = item

    def _build_heap(self):

        ''' Pre: Self.heap has values in 1 to self.heap_size
           Post: Heap property is satisfied for entire heap. '''

        # 1 through self.heap_size.

        for i in range(self.heap_size // 2, 0, -1): # Stops at 1.
            self._heapify(i)

    def heapsort(self):

        '''Pre: Heap Property is satisfied.
           Post: Items are sorted in self.heap[1:self.sorted_size].'''

        sorted_size = self.heap_size

        for i in range(0, sorted_size -1):
            # Since delete_max calls pop to remove an item, we need to append a dummy value to avoid an illegal index.
            self.heap.append(None)
            item = self.delete_max()
            self.heap[sorted_size - i] = item

所以这是有效的，但就像我之前所述，我在如何制作优先级队列方面遇到了麻烦？我知道要求代码是错误的，但我很绝望有人可以帮助我吗？我对我想要的优先级代码做了基本的概述。

#PriorityQueue.py
from MyHeap import Heap


class PriorityQueue(object):

    def enqueue(self, item, priority):
        '''Post: Item is inserted with specified priority in the PQ.'''

    def first(self):
    '''Post: Returns but does not remove the highest priority item from the PQ.'''

    def dequeue(self):
    '''Post: Removes and returns the highest priority item from the PQ.'''

    def size(self):
    '''Post: Returns the number of items in the PQ.'''
        return Heap.heap_size

Answer 1

我认为您实现PriorityQueue类时缺少的关键想法是每个PriorityQueue实例都应该有一个Heap实例作为属性。在__init__：

中进行设置

class PriorityQueue(object):
    def __init__(self)
        self.heap = Heap()

当用户调用PriorityQueue方法时，该方法通常只调用self.heap的方法，只需要一些额外的工作来修改参数或返回值。 insert到堆中的项应该是(priority, value)个元组，因为它们会相应地进行比较（更高优先级的项比较高）。

请注意，如果将为heapq编写的代码与Heap进行比较，则需要修改索引和优先级的逻辑，因为heapq实现了零 - indexed min-heap，你的代码实现了一个索引的最大堆。

使用Heap创建优先级队列。不使用“queue”或“heapq”

1 个答案: