Python/data_structures/LinkedList/DoublyLinkedList.py
2016-11-29 13:44:09 +00:00

73 lines
2.6 KiB
Python

'''
- 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.
- Each link references the next link and the previous one.
'''
class LinkedList:
def __init__(self):
self.head = None
self.tail = None
def insertHead(self, x):
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
self.tail = newLink
else:
self.head.previous = newLink # newLink <-- currenthead(head)
newLink.next = self.head # newLink <--> currenthead(head)
self.head = newLink # newLink(head) <--> oldhead
def deleteHead(self):
temp = self.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
if(self.head == None):
self.tail = None
return temp
def insertTail(self, x):
newLink = Link(x)
newLink.next = None # currentTail(tail) newLink -->
self.tail.next = newLink # currentTail(tail) --> newLink -->
newLink.previous = self.tail #currentTail(tail) <--> newLink -->
self.tail = newLink # oldTail <--> newLink(tail) -->
def deleteTail(self):
temp = self.tail
self.tail = self.tail.previous # 2ndLast(tail) <--> oldTail --> None
self.tail.next = None # 2ndlast(tail) --> None
return temp
def delete(self, x):
current = self.head
while(current.value != x): # Find the position to delete
current = current.next
if(current == self.head):
self.deleteHead()
elif(current == self.tail):
self.deleteTail()
else: #Before: 1 <--> 2(current) <--> 3
current.previous.next = current.next # 1 --> 3
current.next.previous = current.previous # 1 <--> 3
def isEmpty(self): #Will return True if the list is empty
return(self.head == None)
def display(self): #Prints contents of the list
current = self.head
while(current != None):
current.displayLink()
current = current.next
print()
class 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
def __init__(self, x):
self.value = x
def displayLink(self):
print("{}".format(self.value), end=" ")