Python标准库恶补一番

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本文深入探讨Python中三种重要的数据结构与算法：全排列生成、双向队列操作及优先队列应用。通过具体代码实例，详细解析了itertools.permutations生成全排列、collections.deque实现双向队列及heapq构建优先队列的方法。

文章目录

1. 全排列 - itertools.permutations
2. 双向队列 - collections.deque
3. 优先队列 - heapq

1. 全排列 - itertools.permutations

注：Python产生的全排列是会含有重复的项的！并且当且仅当输入的列表是升序的，结果才是按字典序的！

from itertools import permutations

a = [1, 2, 4]
perm = permutations(a)
print(type(perm))
''' <class 'itertools.permutations'> '''
for item in perm:
    print(item)
'''
(1, 2, 4)
(1, 4, 2)
(2, 1, 4)
(2, 4, 1)
(4, 1, 2)
(4, 2, 1)
'''

b = [1, 2, 2, 3]
for item in permutations(b):
    print(item)
'''
(1, 2, 2, 3)
(1, 2, 3, 2)
(1, 2, 2, 3)
(1, 2, 3, 2)
(1, 3, 2, 2)
(1, 3, 2, 2)
(2, 1, 2, 3)
(2, 1, 3, 2)
(2, 2, 1, 3)
(2, 2, 3, 1)
(2, 3, 1, 2)
(2, 3, 2, 1)
(2, 1, 2, 3)
(2, 1, 3, 2)
(2, 2, 1, 3)
(2, 2, 3, 1)
(2, 3, 1, 2)
(2, 3, 2, 1)
(3, 1, 2, 2)
(3, 1, 2, 2)
(3, 2, 1, 2)
(3, 2, 2, 1)
(3, 2, 1, 2)
(3, 2, 2, 1)
'''

2. 双向队列 - collections.deque

from collections import deque

a = deque()

a.append(2)
a.append(3)
a.append(4)
a.appendleft(1)
print(a)
''' deque([1, 2, 3, 4]) '''

print(a.pop())
''' 4 '''
print(a.popleft())
''' 1 '''
print(a)
''' deque([2, 3]) '''

3. 优先队列 - heapq

import heapq

# heappush()：入队
# heappop()：出队
arr = [1, 4, 2, 8, 5, 7]
heap = []
for val in arr:
    heapq.heappush(heap, val)
while heap:
    print(heapq.heappop(heap))
'''
1
2
4
5
7
8
'''

# heapify()：将数组原地转化为优先队列
# heap[0]：获取最小元素
arr = [1, 4, 2, 8, 5, 7]
heapq.heapify(arr)
print(arr[0])
while arr:
    print(heapq.heappop(arr))
'''
1
2
4
5
7
8
'''