python heapq 堆

import heapq
# 第一种
"""
函数定义：
heapq.heappush(heap, item)
- Push the value item onto the heap, maintaining the heap invariant.
heapq.heappop(heap)
- Pop and return the smallest item from the heap, maintaining the heap invariant.
If the heap is empty, IndexError is raised. To access the smallest item without popping it, use heap[0].
"""
nums = [2, 3, 5, 1, 54, 23, 132]
heap = []
for num in nums:
heapq.heappush(heap, num) # 加入堆
print(heap[0]) # 如果只是想获取最小值而不是弹出，使用heap[0]
print([heapq.heappop(heap) for _ in range(len(nums))]) # 堆排序结果
# out: [1, 2, 3, 5, 23, 54, 132]
# 第二种
nums = [2, 3, 5, 1, 54, 23, 132]
heapq.heapify(nums)
print([heapq.heappop(heap) for _ in range(len(nums))]) # 堆排序结果
# out: [1, 2, 3, 5, 23, 54, 132]

"""
函数定义：
heapq.merge(*iterables)
- Merge multiple sorted inputs into a single sorted output (for example, merge timestamped entries from multiple log files). Returns an
iterator over the sorted values.
- Similar to sorted(itertools.chain(*iterables)) but returns an iterable, does not pull the data into memory all at once, and assumes
that each of the input streams is already sorted (smallest to largest).
"""
import heapq
num1 = [32, 3, 5, 34, 54, 23, 132]
num2 = [23, 2, 12, 656, 324, 23, 54]
num1 = sorted(num1)
num2 = sorted(num2)

res = heapq.merge(num1, num2)
print(list(res))

import heapq
nums = [2, 43, 45, 23, 12]
heapq.heapify(nums)
print(heapq.heappop(nums))
# out: 2
# 如果需要所有堆排序后的元素
result = [heapq.heappop(nums) for _ in range(len(nums))]
print(result)
# out: [12, 23, 43, 45]

import heapq
nums = [1, 2, 4, 5, 3]
heapq.heapify(nums)
heapq.heapreplace(nums, 23)
print([heapq.heappop(nums) for _ in range(len(nums))])
# out: [2, 3, 4, 5, 23]

"""
函数定义：
heapq.nlargest(n, iterable[, key])¶
- Return a list with the n largest elements from the dataset defined by iterable.
- key if provided, specifies a function of one argument that is used to extract a comparison key from each element in the iterable: key=str.lower
- Equivalent to: sorted(iterable, key=key, reverse=True)[:n]
"""
import heapq

nums = [1, 3, 4, 5, 2]
print(heapq.nlargest(3, nums))
print(heapq.nsmallest(3, nums))

"""
输出：
[5, 4, 3]
[1, 2, 3]
"""

import heapq
from pprint import pprint
portfolio = [
{'name': 'IBM', 'shares': 100, 'price': 91.1},
{'name': 'AAPL', 'shares': 50, 'price': 543.22},
{'name': 'FB', 'shares': 200, 'price': 21.09},
{'name': 'HPQ', 'shares': 35, 'price': 31.75},
{'name': 'YHOO', 'shares': 45, 'price': 16.35},
{'name': 'ACME', 'shares': 75, 'price': 115.65}
]
cheap = heapq.nsmallest(3, portfolio, key=lambda s: s['price'])
expensive = heapq.nlargest(3, portfolio, key=lambda s: s['price'])
pprint(cheap)
pprint(expensive)

"""
输出：
[{'name': 'YHOO', 'price': 16.35, 'shares': 45},
{'name': 'FB', 'price': 21.09, 'shares': 200},
{'name': 'HPQ', 'price': 31.75, 'shares': 35}]
[{'name': 'AAPL', 'price': 543.22, 'shares': 50},
{'name': 'ACME', 'price': 115.65, 'shares': 75},
{'name': 'IBM', 'price': 91.1, 'shares': 100}]
"""

>>> def heapsort(iterable):
... h = []
... for value in iterable:
... heappush(h, value)
... return [heappop(h) for i in range(len(h))]
...
>>> heapsort([1, 3, 5, 7, 9, 2, 4, 6, 8, 0])
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> h = []
>>> heappush(h, (5, 'write code'))
>>> heappush(h, (7, 'release product'))
>>> heappush(h, (1, 'write spec'))
>>> heappush(h, (3, 'create tests'))
>>> heappop(h)
(1, 'write spec')