Rotate Doubly Linked List Python

PROGRAM TO ROTATE DOUBLY LINKED LIST BY N NODES

class Node: 

    def __init__(self, next = None, 

                       prev = None, data = None): 

        self.next = next # reference to next node in DLL 

        self.prev = prev # reference to previous node in DLL 

        self.data = data 

  

def push(head, new_data): 

  

    new_node = Node(data = new_data) 

  

    new_node.next = head 

    new_node.prev = None

  

    if head is not None: 

        head.prev = new_node 

  

    head = new_node

    return head

  

def printList(head):

  

    node = head

  

    print("Given linked list")

    while(node is not None): 

        print(node.data, end = " "), 

        last = node 

        node = node.next

      

def rotate(start, N):

    if N == 0 :

        return

  

    # Let us understand the below code 

    # for example N = 2 and 

    # list = a <-> b <-> c <-> d <-> e. 

    current = start 

  

    # current will either point to Nth 

    # or None after this loop. Current 

    # will point to node 'b' in the 

    # above example 

    count = 1

    while count < N and current != None :

        current = current.next

        count += 1

  

    # If current is None, N is greater 

    # than or equal to count of nodes 

    # in linked list. Don't change the 

    # list in this case 

    if current == None :

        return

  

    # current points to Nth node. Store 

    # it in a variable. NthNode points to 

    # node 'b' in the above example 

    NthNode = current 

  

    # current will point to last node 

    # after this loop current will point 

    # to node 'e' in the above example 

    while current.next != None :

        current = current.next

  

    # Change next of last node to previous 

    # head. Next of 'e' is now changed to 

    # node 'a' 

    current.next = start 

  

    # Change prev of Head node to current 

    # Prev of 'a' is now changed to node 'e' 

    start.prev = current 

  

    # Change head to (N+1)th node 

    # head is now changed to node 'c' 

    start = NthNode.next

  

    # Change prev of New Head node to None 

    # Because Prev of Head Node in Doubly 

    # linked list is None 

    start.prev = None

  

    # change next of Nth node to None 

    # next of 'b' is now None 

    NthNode.next = None

  

    return start

  

# Driver Code

if __name__ == "__main__":

    head = None

  

    head = push(head, 'e')

    head = push(head, 'd')

    head = push(head, 'c')

    head = push(head, 'b')

    head = push(head, 'a')

  

    printList(head)

    print("\n")

      

    N = 2

    head = rotate(head, N)

  

    printList(head)

OUTPUT:

Given linked list 
a  b  c  d  e
Rotated Linked list 
c  d  e  a  b

CREDITS: https://www.geeksforgeeks.org/rotate-doubly-linked-list-n-nodes/