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77 lines
2.7 KiB
Python
77 lines
2.7 KiB
Python
'''
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- A linked list is similar to an array, it holds values. However, links in a linked list do not have indexes.
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- This is an example of a double ended, doubly linked list.
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- Each link references the next link and the previous one.
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'''
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from __future__ import print_function
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class LinkedList:
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def __init__(self):
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self.head = None
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self.tail = None
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def insertHead(self, x):
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newLink = Link(x) #Create a new link with a value attached to it
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if(self.isEmpty() == True): #Set the first element added to be the tail
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self.tail = newLink
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else:
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self.head.previous = newLink # newLink <-- currenthead(head)
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newLink.next = self.head # newLink <--> currenthead(head)
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self.head = newLink # newLink(head) <--> oldhead
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def deleteHead(self):
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temp = self.head
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self.head = self.head.next # oldHead <--> 2ndElement(head)
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self.head.previous = None # oldHead --> 2ndElement(head) nothing pointing at it so the old head will be removed
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if(self.head is None):
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self.tail = None
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return temp
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def insertTail(self, x):
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newLink = Link(x)
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newLink.next = None # currentTail(tail) newLink -->
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self.tail.next = newLink # currentTail(tail) --> newLink -->
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newLink.previous = self.tail #currentTail(tail) <--> newLink -->
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self.tail = newLink # oldTail <--> newLink(tail) -->
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def deleteTail(self):
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temp = self.tail
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self.tail = self.tail.previous # 2ndLast(tail) <--> oldTail --> None
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self.tail.next = None # 2ndlast(tail) --> None
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return temp
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def delete(self, x):
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current = self.head
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while(current.value != x): # Find the position to delete
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current = current.next
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if(current == self.head):
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self.deleteHead()
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elif(current == self.tail):
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self.deleteTail()
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else: #Before: 1 <--> 2(current) <--> 3
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current.previous.next = current.next # 1 --> 3
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current.next.previous = current.previous # 1 <--> 3
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def isEmpty(self): #Will return True if the list is empty
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return(self.head is None)
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def display(self): #Prints contents of the list
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current = self.head
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while(current != None):
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current.displayLink()
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current = current.next
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print()
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class Link:
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next = None #This points to the link in front of the new link
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previous = None #This points to the link behind the new link
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def __init__(self, x):
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self.value = x
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def displayLink(self):
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print("{}".format(self.value), end=" ")
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