Python - Insert a new node at the end of the Circular Doubly Linked List

In this method, a new node is inserted at the end of the circular doubly linked list. For example - if the given List is 10->20->30 and a new element 100 is added at the end, the List becomes 10->20->30->100.

Inserting a new node at the end of the circular doubly linked list is very easy. First, a new node with given element is created. It is then added at the end of the list by linking the last node and head node to the new node.

Circular Doubly Linked List - Add Node At End

The function push_back is created for this purpose. It is a 6-step process.

def push_back(self, newElement):
  
  #1 & 2 & 3. allocate node, assign data element
  #          assign null to the next and prev of 
  #          the new node
  newNode = Node(newElement)
  
  #4. Check the list is empty or not,
  #   if empty make the new node as head 
  if(self.head == None):
    self.head = newNode
    newNode.next = self.head
    newNode.prev = self.head
    return
  else:
    
    #5. Else, traverse to the last node
    temp = self.head
    while(temp.next != self.head):
      temp = temp.next
    
    #6. Adjust the links  
    temp.next = newNode
    newNode.next = self.head
    newNode.prev = temp
    self.head.prev = newNode

The below is a complete program that uses above discussed concept to insert new node at the end of the circular doubly linked list.

# node structure
class Node:
  def __init__(self, data):
    self.data = data
    self.next = None
    self.prev = None

#class Linked List
class LinkedList:
  def __init__(self):
    self.head = None

  #Add new element at the end of the list
  def push_back(self, newElement):
    newNode = Node(newElement)
    if(self.head == None):
      self.head = newNode
      newNode.next = self.head
      newNode.prev = self.head
      return
    else:
      temp = self.head
      while(temp.next != self.head):
        temp = temp.next
      temp.next = newNode
      newNode.next = self.head
      newNode.prev = temp
      self.head.prev = newNode

  #display the content of the list
  def PrintList(self):
    temp = self.head
    if(temp != None):
      print("The list contains:", end=" ")
      while (True):
        print(temp.data, end=" ")
        temp = temp.next
        if(temp == self.head):
          break
      print()
    else:
      print("The list is empty.")

# test the code                  
MyList = LinkedList()

#Add three elements at the end of the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)
MyList.PrintList()

The above code will give the following output:

The list contains: 10 20 30