Python包含了用于min-堆的heapq模块,但我需要一个max堆。在Python中我应该使用什么来实现最大堆?
当前回答
你可以使用
import heapq
listForTree = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
heapq.heapify(listForTree) # for a min heap
heapq._heapify_max(listForTree) # for a maxheap!!
如果你想要弹出元素,使用:
heapq.heappop(minheap) # pop from minheap
heapq._heappop_max(maxheap) # pop from maxheap
其他回答
解决方案是当你在堆中存储你的值时对其求反,或者像这样反转你的对象比较:
import heapq
class MaxHeapObj(object):
def __init__(self, val): self.val = val
def __lt__(self, other): return self.val > other.val
def __eq__(self, other): return self.val == other.val
def __str__(self): return str(self.val)
max-heap的例子:
maxh = []
heapq.heappush(maxh, MaxHeapObj(x))
x = maxh[0].val # fetch max value
x = heapq.heappop(maxh).val # pop max value
但是您必须记住包装和打开您的值,这需要知道您正在处理的是最小堆还是最大堆。
MinHeap, MaxHeap类
为MinHeap和MaxHeap对象添加类可以简化代码:
class MinHeap(object):
def __init__(self): self.h = []
def heappush(self, x): heapq.heappush(self.h, x)
def heappop(self): return heapq.heappop(self.h)
def __getitem__(self, i): return self.h[i]
def __len__(self): return len(self.h)
class MaxHeap(MinHeap):
def heappush(self, x): heapq.heappush(self.h, MaxHeapObj(x))
def heappop(self): return heapq.heappop(self.h).val
def __getitem__(self, i): return self.h[i].val
使用示例:
minh = MinHeap()
maxh = MaxHeap()
# add some values
minh.heappush(12)
maxh.heappush(12)
minh.heappush(4)
maxh.heappush(4)
# fetch "top" values
print(minh[0], maxh[0]) # "4 12"
# fetch and remove "top" values
print(minh.heappop(), maxh.heappop()) # "4 12"
我实现了一个最大堆版本的heapq,并将它提交给PyPI。(对heapq模块CPython代码的改动很小。)
https://pypi.python.org/pypi/heapq_max/
https://github.com/he-zhe/heapq_max
安装
pip install heapq_max
使用
dr:与heapq模块相同,只是所有函数都增加了' _max '。
heap_max = [] # creates an empty heap
heappush_max(heap_max, item) # pushes a new item on the heap
item = heappop_max(heap_max) # pops the largest item from the heap
item = heap_max[0] # largest item on the heap without popping it
heapify_max(x) # transforms list into a heap, in-place, in linear time
item = heapreplace_max(heap_max, item) # pops and returns largest item, and
# adds new item; the heap size is unchanged
arr = [3,4,5,1,2,3,0,7,8,90,67,31,2,5,567]
# max-heap sort will lead the array to assending order
def maxheap(arr,p):
for i in range(len(arr)-p):
if i > 0:
child = i
parent = (i+1)//2 - 1
while arr[child]> arr[parent] and child !=0:
arr[child], arr[parent] = arr[parent], arr[child]
child = parent
parent = (parent+1)//2 -1
def heapsort(arr):
for i in range(len(arr)):
maxheap(arr,i)
arr[0], arr[len(arr)-i-1]=arr[len(arr)-i-1],arr[0]
return arr
print(heapsort(arr))
试试这个
如果你想用max heap得到最大的K元素,你可以做下面的技巧:
nums= [3,2,1,5,6,4]
k = 2 #k being the kth largest element you want to get
heapq.heapify(nums)
temp = heapq.nlargest(k, nums)
return temp[-1]
最简单的方法是反转键的值并使用heapq。例如,将1000.0转换为-1000.0,将5.0转换为-5.0。
推荐文章
- 证书验证失败:无法获得本地颁发者证书
- 当使用pip3安装包时,“Python中的ssl模块不可用”
- 无法切换Python与pyenv
- Python if not == vs if !=
- 如何从scikit-learn决策树中提取决策规则?
- 为什么在Mac OS X v10.9 (Mavericks)的终端中apt-get功能不起作用?
- 将旋转的xtick标签与各自的xtick对齐
- 为什么元组可以包含可变项?
- 如何合并字典的字典?
- 如何创建类属性?
- 不区分大小写的“in”
- 在Python中获取迭代器中的元素个数
- 解析日期字符串并更改格式
- 使用try和。Python中的if
- 如何在Python中获得所有直接子目录