doubly linked list python code example

Example 1: doubly linked list in python

Full implementation of Doubly Linked List:

https://github.com/shreyasvedpathak/Data-Structure-Python/tree/master/LinkedList

Example 2: doubly linked list python

class ListNode:
    def __init__(self, value, prev=None, next=None):
        self.prev = prev
        self.value = value
        self.next = next

class DoublyLinkedList:
    def __init__(self, node=None):
        self.head = node
        self.tail = node
        self.length = 1 if node is not None else 0

    def __len__(self):
        return self.length
   
  	def add_to_head(self, value):
        new_node = ListNode(value, None, None)
        self.length += 1
        if not self.head and not self.tail:
            self.head = new_node
            self.tail = new_node
        else:
            new_node.next = self.head
            self.head.prev = new_node
            self.head = new_node
 
    def remove_from_head(self):
        value = self.head.value
        self.delete(self.head)
        return value

    def add_to_tail(self, value):
        new_node = ListNode(value, None, None)
        self.length += 1
        if not self.tail and not self.head:
            self.tail = new_node
            self.head = new_node
        else:
            new_node.prev = self.tail
            self.tail.next = new_node
            self.tail = new_node
            

    def remove_from_tail(self):
        value = self.tail.value
        self.delete(self.tail)
        return value
            
    def move_to_front(self, node):
        if node is self.head:
            return
        value = node.value
        if node is self.tail:
            self.remove_from_tail()
        else:
            node.delete()
            self.length -= 1
        self.add_to_head(value)
        
    def move_to_end(self, node):
        if node is self.tail:
            return
        value = node.value
        if node is self.head:
            self.remove_from_head()
            self.add_to_tail(value)
        else:
            node.delete()
            self.length -= 1
            self.add_to_tail(value)

    def delete(self, node):
        self.length -= 1
        if not self.head and not self.tail:
            return
        if self.head == self.tail:
            self.head = None
            self.tail = None
        elif self.head == node:
            self.head = node.next
            node.delete()
        elif self.tail == node:
            self.tail = node.prev
            node.delete()
        else:
            node.delete()

    def get_max(self):
        if not self.head:
            return None
        max_val = self.head.value
        current = self.head
        while current:
            if current.value > max_val:
                max_val = current.value
            current = current.next
        return max_val

Example 3: doubly linked list python

# Initialise the Node
class Node:
    def __init__(self, data):
        self.item = data
        self.next = None
        self.prev = None
# Class for doubly Linked List
class doublyLinkedList:
    def __init__(self):
        self.start_node = None
    # Insert Element to Empty list
    def InsertToEmptyList(self, data):
        if self.start_node is None:
            new_node = Node(data)
            self.start_node = new_node
        else:
            print("The list is empty")
    # Insert element at the end
    def InsertToEnd(self, data):
        # Check if the list is empty
        if self.start_node is None:
            new_node = Node(data)
            self.start_node = new_node
            return
        n = self.start_node
        # Iterate till the next reaches NULL
        while n.next is not None:
            n = n.next
        new_node = Node(data)
        n.next = new_node
        new_node.prev = n
    # Delete the elements from the start
    def DeleteAtStart(self):
        if self.start_node is None:
            print("The Linked list is empty, no element to delete")
            return 
        if self.start_node.next is None:
            self.start_node = None
            return
        self.start_node = self.start_node.next
        self.start_prev = None;
    # Delete the elements from the end
    def delete_at_end(self):
        # Check if the List is empty
        if self.start_node is None:
            print("The Linked list is empty, no element to delete")
            return 
        if self.start_node.next is None:
            self.start_node = None
            return
        n = self.start_node
        while n.next is not None:
            n = n.next
        n.prev.next = None
    # Traversing and Displaying each element of the list
    def Display(self):
        if self.start_node is None:
            print("The list is empty")
            return
        else:
            n = self.start_node
            while n is not None:
                print("Element is: ", n.item)
                n = n.next
        print("\n")
# Create a new Doubly Linked List
NewDoublyLinkedList = doublyLinkedList()
# Insert the element to empty list
NewDoublyLinkedList.InsertToEmptyList(10)
# Insert the element at the end
NewDoublyLinkedList.InsertToEnd(20)
NewDoublyLinkedList.InsertToEnd(30)
NewDoublyLinkedList.InsertToEnd(40)
NewDoublyLinkedList.InsertToEnd(50)
NewDoublyLinkedList.InsertToEnd(60)
# Display Data
NewDoublyLinkedList.Display()
# Delete elements from start
NewDoublyLinkedList.DeleteAtStart()
# Delete elements from end
NewDoublyLinkedList.DeleteAtStart()
# Display Data
NewDoublyLinkedList.Display()