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82 lines
2.9 KiB
Python
82 lines
2.9 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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- 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.
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- Advantages over SLL - IT can be traversed in both forward and backward direction.,Delete operation is more efficent"""
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class LinkedList: # making main class named linked list
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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 = (
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None
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) # 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 # if empty linked list
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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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