Python中的双端队列详解 _Python开发

Python中的双端队列(双端队列)是使用模块collections。 Deque优先于list在我们需要从容器的两端更快地执行添加和弹出操作的情况下, 因为双端队列提供了O(1)与提供O(n)时间复杂度的列表相比, 追加和弹出操作的时间复杂度。
例子：

# Python code to demonstrate deque from collections import deque # Declaring deque queue = deque([ 'name' , 'age' , 'DOB' ])print (queue)

输出如下：

deque(['name', 'age', 'DOB'])

让我们看一下双端队列的各种操作：
append()：-此函数用于将值插入到双端队列的右端。
appendleft()：-此函数用于将其值插入到双端队列的左端。
pop()：-此函数用于从双端队列的右端删除一个参数。
popleft()：-此函数用于从双端队列的左端删除一个参数。

# Python code to demonstrate working of # append(), appendleft(), pop(), and popleft()# importing "collections" for deque operations import collections# initializing deque de = collections.deque([ 1 , 2 , 3 ])# using append() to insert element at right end # inserts 4 at the end of deque de.append( 4 )# printing modified deque print ( "The deque after appending at right is : " ) print (de)# using appendleft() to insert element at right end # inserts 6 at the beginning of deque de.appendleft( 6 )# printing modified deque print ( "The deque after appending at left is : " ) print (de)# using pop() to delete element from right end # deletes 4 from the right end of deque de.pop()# printing modified deque print ( "The deque after deleting from right is : " ) print (de)# using popleft() to delete element from left end # deletes 6 from the left end of deque de.popleft()# printing modified deque print ( "The deque after deleting from left is : " ) print (de)

输出如下：

The deque after appending at right is : deque([1, 2, 3, 4]) The deque after appending at left is : deque([6, 1, 2, 3, 4]) The deque after deleting from right is : deque([6, 1, 2, 3]) The deque after deleting from left is : deque([1, 2, 3])

index(ele, beg, end)：-此函数返回参数中提到的值的第一个索引, 从beg开始搜索, 直到结束索引。
insert(i, a)：-此函数将在arguments(a)中提到的值插入到arguments中指定的索引(i)。
去掉()
：-此功能
删除第一次出现
论据中提到的价值。
count()：-此函数计算参数中提到的值的出现次数。

# Python code to demonstrate working of # insert(), index(), remove(), count()# importing "collections" for deque operations import collections# initializing deque de = collections.deque([ 1 , 2 , 3 , 3 , 4 , 2 , 4 ])# using index() to print the first occurrence of 4 print ( "The number 4 first occurs at a position : " ) print (de.index( 4 , 2 , 5 ))# using insert() to insert the value 3 at 5th position de.insert( 4 , 3 )# printing modified deque print ( "The deque after inserting 3 at 5th position is : " ) print (de)# using count() to count the occurrences of 3 print ( "The count of 3 in deque is : " ) print (de.count( 3 ))# using remove() to remove the first occurrence of 3 de.remove( 3 )# printing modified deque print ( "The deque after deleting first occurrence of 3 is : " ) print (de)

输出如下：

The number 4 first occurs at a position : 4 The deque after inserting 3 at 5th position is : deque([1, 2, 3, 3, 3, 4, 2, 4]) The count of 3 in deque is : 3 The deque after deleting first occurrence of 3 is : deque([1, 2, 3, 3, 4, 2, 4])

extend(iterable)：-此函数用于在双端队列的右端添加多个值。传递的参数是可迭代的。
extendleft(iterable)：-此函数用于在双端队列的左端添加多个值。传递的参数是可迭代的。由于左侧追加, 顺序颠倒了。
reverse()：-此函数用于反转双端队列元素的顺序。
rotation()：-此函数将双端队列旋转由参数指定的数字。如果指定的数字为负, 则向左旋转。其他旋转向右。

# Python code to demonstrate working of # extend(), extendleft(), rotate(), reverse()# importing "collections" for deque operations import collections# initializing deque de = collections.deque([ 1 , 2 , 3 , ])# using extend() to add numbers to right end # adds 4, 5, 6 to right end de.extend([ 4 , 5 , 6 ])# printing modified deque print ( "The deque after extending deque at end is : " ) print (de)# using extendleft() to add numbers to left end # adds 7, 8, 9 to right end de.extendleft([ 7 , 8 , 9 ])# printing modified deque print ( "The deque after extending deque at beginning is : " ) print (de)# using rotate() to rotate the deque # rotates by 3 to left de.rotate( - 3 )# printing modified deque print ( "The deque after rotating deque is : " ) print (de)# using reverse() to reverse the deque de.reverse()# printing modified deque print ( "The deque after reversing deque is : " ) print (de)

输出：

The deque after extending deque at end is : deque([1, 2, 3, 4, 5, 6]) The deque after extending deque at beginning is : deque([9, 8, 7, 1, 2, 3, 4, 5, 6]) The deque after rotating deque is : deque([1, 2, 3, 4, 5, 6, 9, 8, 7]) The deque after reversing deque is : deque([7, 8, 9, 6, 5, 4, 3, 2, 1])

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