Question

implement the reverse() method that changes the ordering of the items within a doublylinkedlist class. don't return anything and make sure it executes without errors on lists with no items or one item

example:

fruits = DoublyLinkedList()
fruits.append('apple')
fruits.append('banana')
fruits.append('cherry')
for i in fruits:
    print(i)
>> apple
>> banana
>> Charlie

fruits.reverse()
for i in fruits:
    print(i)
>> cherry
>> banana
>> apple

Answer 1

Code:

class Node:
  
# Constructor to create a new node
def __init__(self, data):
self.data = data
self.next = None
self.prev = None
  
class DoublyLinkedList:
# Constructor for empty Doubly Linked List
def __init__(self):
self.head = None

# Function reverse a Doubly Linked List
def reverse(self):
temp = None
current = self.head
  
# Swap next and prev for all nodes of
# doubly linked list
while current is not None:
temp = current.prev
current.prev = current.next
current.next = temp
current = current.prev
  
# Before changing head, check for the cases like
# empty list and list with only one node
if temp is not None:
self.head = temp.prev
  
# Given a reference to the head of a list and an
# integer,inserts a new node on the front of list
def push(self, new_data):

# 1. Allocates node
# 2. Put the data in it
new_node = Node(new_data)

# 3. Make next of new node as head and
# previous as None (already None)
new_node.next = self.head

# 4. change prev of head node to new_node
if self.head is not None:
self.head.prev = new_node

# 5. move the head to point to the new node
self.head = new_node
  
  
def printList(self, node):
while(node is not None):
print(node.data)
node = node.next
  
# Driver program to test the above functions
dll = DoublyLinkedList()
dll.push("Apple");
dll.push("Banana");
dll.push("Cherry");
  
print("\nOriginal Linked List:\n")
dll.printList(dll.head)
  
# Reverse doubly linked list
dll.reverse()
  
print("\n\nReversed Linked List:\n")
dll.printList(dll.head)

Note: refer the screenshots for indentation purposes