Python中的双端队列

Python中的 Deque（双端队列）是使用模块“集合”实现的。在我们需要从容器两端进行更快的追加和弹出操作的情况下，双端队列优于列表，因为与提供 O(n) 的列表相比，双端队列为追加和弹出操作提供O(1)时间复杂度时间复杂度。

例子：

Python3

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

输出：

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

让我们看看 deque 上的各种操作：

• append() :- 此函数用于将其参数中的值插入到双端队列的右端。
• appendleft() :- 该函数用于将其参数中的值插入到双端队列的左端。
• pop() :- 该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。

Python3

# 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 left 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：

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 arguments(a) 中提到的值插入arguments 中指定的index(i) 处。
• remove() :- 此函数删除参数中提到的第一次出现的值。
• count() :- 此函数计算参数中提到的值的出现次数。

Python3

# 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：

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) :- 该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) :- 该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。由于左附加，顺序颠倒了。
• reverse() :- 此函数用于反转双端队列元素的顺序。
• rotate() :- 此函数将双端队列旋转参数中指定的数量。如果指定的数字为负数，则向左旋转。否则旋转向右。

Python3

# 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 left 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])