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Update doubly_linked_list.py (#545)

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Aditya Sharma 2018-10-31 13:04:55 +05:30 committed by Harshil
parent 6db1994de2
commit 1b19028117
1 changed files with 22 additions and 21 deletions
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43
data_structures/linked_list/doubly_linked_list.py
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@ -2,49 +2,50 @@
- A linked list is similar to an array, it holds values. However, links in a linked list do not have indexes. - A linked list is similar to an array, it holds values. However, links in a linked list do not have indexes.
- This is an example of a double ended, doubly linked list. - This is an example of a double ended, doubly linked list.
- Each link references the next link and the previous one. - Each link references the next link and the previous one.
''' - A Doubly Linked List (DLL) contains an extra pointer, typically called previous pointer, together with next pointer and data which are there in singly linked list.
- Advantages over SLL - IT can be traversed in both forward and backward direction.,Delete operation is more efficent'''
from __future__ import print_function from __future__ import print_function
class LinkedList: class LinkedList: #making main class named linked list
def __init__(self): def __init__(self):
self.head = None self.head = None
self.tail = None self.tail = None
def insertHead(self, x): def insertHead(self, x):
newLink = Link(x) #Create a new link with a value attached to it newLink = Link(x) #Create a new link with a value attached to it
if(self.isEmpty() == True): #Set the first element added to be the tail if(self.isEmpty() == True): #Set the first element added to be the tail
self.tail = newLink self.tail = newLink
else: else:
self.head.previous = newLink # newLink <-- currenthead(head) self.head.previous = newLink # newLink <-- currenthead(head)
newLink.next = self.head # newLink <--> currenthead(head) newLink.next = self.head # newLink <--> currenthead(head)
self.head = newLink # newLink(head) <--> oldhead self.head = newLink # newLink(head) <--> oldhead
def deleteHead(self): def deleteHead(self):
temp = self.head temp = self.head
self.head = self.head.next # oldHead <--> 2ndElement(head) self.head = self.head.next # oldHead <--> 2ndElement(head)
self.head.previous = None # oldHead --> 2ndElement(head) nothing pointing at it so the old head will be removed self.head.previous = None # oldHead --> 2ndElement(head) nothing pointing at it so the old head will be removed
if(self.head is None): if(self.head is None):
self.tail = None self.tail = None #if empty linked list
return temp return temp
def insertTail(self, x): def insertTail(self, x):
newLink = Link(x) newLink = Link(x)
newLink.next = None # currentTail(tail) newLink --> newLink.next = None # currentTail(tail) newLink -->
self.tail.next = newLink # currentTail(tail) --> newLink --> self.tail.next = newLink # currentTail(tail) --> newLink -->
newLink.previous = self.tail #currentTail(tail) <--> newLink --> newLink.previous = self.tail #currentTail(tail) <--> newLink -->
self.tail = newLink # oldTail <--> newLink(tail) --> self.tail = newLink # oldTail <--> newLink(tail) -->
def deleteTail(self): def deleteTail(self):
temp = self.tail temp = self.tail
self.tail = self.tail.previous # 2ndLast(tail) <--> oldTail --> None self.tail = self.tail.previous # 2ndLast(tail) <--> oldTail --> None
self.tail.next = None # 2ndlast(tail) --> None self.tail.next = None # 2ndlast(tail) --> None
return temp return temp
def delete(self, x): def delete(self, x):
current = self.head current = self.head
while(current.value != x): # Find the position to delete while(current.value != x): # Find the position to delete
current = current.next current = current.next
if(current == self.head): if(current == self.head):
@ -57,10 +58,10 @@ class LinkedList:
current.previous.next = current.next # 1 --> 3 current.previous.next = current.next # 1 --> 3
current.next.previous = current.previous # 1 <--> 3 current.next.previous = current.previous # 1 <--> 3
def isEmpty(self): #Will return True if the list is empty def isEmpty(self): #Will return True if the list is empty
return(self.head is None) return(self.head is None)
def display(self): #Prints contents of the list def display(self): #Prints contents of the list
current = self.head current = self.head
while(current != None): while(current != None):
current.displayLink() current.displayLink()
@ -68,8 +69,8 @@ class LinkedList:
print() print()
class Link: class Link:
next = None #This points to the link in front of the new link next = None #This points to the link in front of the new link
previous = None #This points to the link behind the new link previous = None #This points to the link behind the new link
def __init__(self, x): def __init__(self, x):
self.value = x self.value = x
def displayLink(self): def displayLink(self):