# Python - Delete the last node of the Circular Doubly Linked List

In this method, the last node of the circular doubly linked list is deleted. For example - if the given list is 10->20->30->40 and the last node is deleted, the list becomes 10->20->30.

Deleting the last node of the Circular Doubly Linked List involves checking the head for empty. If it is not empty and contains only one node then delete the head node. If the list contains more than one node then traverse to the second last node of the list and link it with the head. Finally, delete the last node.

The function *pop_back* is created for this purpose. It is a **3-step process**.

def pop_back(self): if(self.head != None): #1. if head in not null and next of head # is head, release the head if(self.head.next == self.head): self.head = None else: #2. Else, traverse to the second last # element of the list temp = self.head while(temp.next.next != self.head): temp = temp.next #3. Update links of head and second # last node, and delete the last node lastNode = temp.next temp.next = self.head self.head.prev = temp lastNode = None

The below is a complete program that uses above discussed concept of deleting the last node 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 #Delete last node of the list def pop_back(self): if(self.head != None): if(self.head.next == self.head): self.head = None else: temp = self.head while(temp.next.next != self.head): temp = temp.next lastNode = temp.next temp.next = self.head self.head.prev = temp lastNode = None #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 four elements in the list. MyList.push_back(10) MyList.push_back(20) MyList.push_back(30) MyList.push_back(40) MyList.PrintList() #Delete the last node MyList.pop_back() MyList.PrintList()

The above code will give the following output:

The list contains: 10 20 30 40 The list contains: 10 20 30