Data structures and algorithms implemented by Python: Dual-end queue explanation; python data structures and algorithms

Data structures and algorithms implemented by Python: Dual-end queue explanation; python data structures and algorithms

This article describes the Python-implemented data structure and algorithm dual-end queue. Share it with you for your reference. The specific analysis is as follows:

I. Overview

A double-ended queue (deque) is a linear data structure with queues and stacks. The dual-end queue also has two ends: front and rear. However, unlike the queue, the insert operation can be performed on both ends (first and last, the same is true for delete operations.

Ii. ADT

The dual-end queue ADT (abstract data type) generally provides the following interfaces:

① Deque () creates a dual-end queue
② AddFront (item) inserts an item into the first line
③ AddRear (item) inserts an item to the end of the team
④ RemoveFront () returns the first item and deletes the item from the double-ended queue.
⑤ RemoveRear () returns the item at the end of the team and deletes the item from the dual-end queue.
⑥ Empty () determines whether the dual-end queue is empty
7. size () returns the number of items in the double-ended queue.

The double-end queue operation is as follows:

Iii. Python implementation

In Python, there are two ways to implement the above two-end queue ADT: using the built-in type list, using the standard library collections. deque (actually collections. deque is the standard implementation of double-end queues in Python ).

The two methods differ mainly in performance (For details, refer to collections. deque | TimeComplexity ):

Operation | Implementation list collections.deque
-----------------------------------------
addFront O (n) O (1)
-----------------------------------------
addRear O (1) O (1)
-----------------------------------------
removeFront O (n) O (1)
-----------------------------------------
removeRear O (1) O (1)

1. Use the built-in type list

#!/usr/bin/env python
# -*- coding: utf-8 -*-
class Deque:
  def __init__(self):
    self.items = []
  def addFront(self, item):
    self.items.insert(0, item)
  def addRear(self, item):
    self.items.append(item)
  def removeFront(self):
    return self.items.pop(0)
  def removeRear(self):
    return self.items.pop()
  def empty(self):
    return self.size() == 0
  def size(self):
    return len(self.items)

2. Use the standard library collections. deque

#!/usr/bin/env python
# -*- coding: utf-8 -*-
from collections import deque
class Deque:
  def __init__(self):
    self.items = deque()
  def addFront(self, item):
    self.items.appendleft(item)
  def addRear(self, item):
    self.items.append(item)
  def removeFront(self):
    return self.items.popleft()
  def removeRear(self):
    return self.items.pop()
  def empty(self):
    return self.size() == 0
  def size(self):
    return len(self.items)

Iv. Application

Palindrome (palindrome) is a rhetorical and text game that shares the same words or sentences as reading and reading.

Example:

Madam
Able was I ere I saw elba

Chinese example:

Hua fehua
Everyone for me, everyone for me
If you want to implement a retrieval Verification Algorithm (to verify whether a given string is a retrieval), it is very easy to use the Deque class: to store the string to the double-end queue, at the same time, take out the first and last characters and compare them to determine whether they are equal. If there is a pair of characters, the string is not a background. If all the characters are equal, the string is a background. The Code is as follows:

#! / usr / bin / env python
#-*-coding: utf-8-*-
def palchecker (aString):
   chardeque = Deque ()
   for ch in aString:
     chardeque.addRear (ch)
   while chardeque.size ()> 1:
     first = chardeque.removeFront ()
     last = chardeque.removeRear ()
     if first! = last:
       return False
   return True
if __name__ == '__main__':
   str1 = 'able was i ere i saw elba'
   print ('"% s" is% s palindrome'% (str1, '' if palchecker (str1) else 'not'))
   str2 = u'Everyone is me, I am everybody '
   print (u '"% s"% s is a palindrome'% (str2, u '' if palchecker (str2) else u '不'))
   str3 = u "What's wrong?"
   print (u '"% s"% s is a palindrome'% (str3, u '' if palchecker (str3) else u '不'))

Running result:

$ python palchecker.py
"able was i ere i saw elba" is palindrome
"Everyone for me, I am for everyone" is the palindrome
"What's wrong?" 

I hope this article will help you with Python programming.