heapq与自定义比较谓词 [英] heapq with custom compare predicate

问题描述

我正在尝试使用自定义排序谓词构建堆。因为进入它的值是用户定义的类型，所以我无法修改其内置的比较谓词。

I am trying to build a heap with a custom sort predicate. Since the values going into it are of 'user-defined' type, I cannot modify their built-in comparison predicate.

有没有办法做到这一点： / p>

Is there a way to do something like:

h = heapq.heapify([...], key=my_lt_pred)
h = heapq.heappush(h, key=my_lt_pred)

或者更好的是，我可以将heapq函数包装在我自己的容器中，所以我不需要继续传递谓词。

Or even better, I could wrap the heapq functions in my own container so I don't need to keep passing the predicate.

推荐答案

根据 heapq文档，自定义堆顺序的方法是将堆上的每个元素都作为元组，第一个元组元素是接受的元组正常的Python比较。

According to the heapq documentation, the way to customize the heap order is to have each element on the heap to be a tuple, with the first tuple element being one that accepts normal Python comparisons.

heapq模块中的函数有点麻烦（因为它们不是面向对象），并且总是需要我们的堆对象（堆叠列表）作为第一个参数被明确传递。通过创建一个非常简单的包装类，我们可以用一块石头杀死两只鸟，这样我们可以指定一个键函数，并将堆呈现为一个对象。

The functions in the heapq module are a bit cumbersome (since they are not object-oriented), and always require our heap object (a heapified list) to be explicitly passed as the first parameter. We can kill two birds with one stone by creating a very simple wrapper class that will allow us to specify a key function, and present the heap as an object.

下面的类保存一个内部列表，其中每个元素是一个元组，其第一个成员是一个键，使用键在元素插入时计算参数，在堆实例化中传递：

The class below keeps an internal list, where each element is a tuple, the first member of which is a key, calculated at element insertion time using the key parameter, passed at Heap instantiation:

# -*- coding: utf-8 -*-
import heapq

class MyHeap(object):
   def __init__(self, initial=None, key=lambda x:x):
       self.key = key
       if initial:
           self._data = [(key(item), item) for item in initial]
           heapq.heapify(self._data)
       else:
           self._data = []

   def push(self, item):
       heapq.heappush(self._data, (self.key(item), item))

   def pop(self):
       return heapq.heappop(self._data)[1]

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