8. Python program to insert a new node at the beginning of the Circular Linked List

In this program, we will create a circular linked list and insert every new node at the beginning of the list. If the list is empty, then head and tail will point to the newly added node. If the list is not empty, then we will store the data of the head into a temporary node temp and make new node as the head. This new head will point to the temporary node. In simple words, the newly added node will be the first node(head) and previous head(temp) will become the second node of the list.

After inserting the new node to the beginning of the list.

New represents the newly added node. Earlier A was the head of the list. When new is added to the beginning of the list, new will become the new head, and it will point to the previous head, i.e., A.

ALGORITHM:

Define a Node class which represents a node in the list. It has two properties data and next which will point to the next node.
Define another class for creating the circular linked list, and it has two nodes: head and tail. It has two methods: addAtStart() and display() .
addAtStart() will add the node to the beginning of the list:

It first checks whether the head is null (empty list), then it will insert the node as the head.
Both head and tail will point to a newly added node.
If the list is not empty, then the newly added node will become the new head, and it will point to the previous head.

a. display() will show all the nodes present in the list.

Define a new node 'current' that will point to the head.
Print current.data till current will points to head again.
Current will point to the next node in the list in each iteration.

PROGRAM:

#Represents the node of list.  
class Node:  
  def __init__(self,data):  
    self.data = data;  
    self.next = None;  
   
class CreateList:  
  #Declaring head and tail pointer as null.  
  def __init__(self):  
    self.head = Node(None);  
    self.tail = Node(None);  
    self.head.next = self.tail;  
    self.tail.next = self.head;  
      
  #This function will add at the start of the list.  
  def addAtStart(self,data):  
    newNode = Node(data);  
    #Checks if the list is empty.  
    if self.head.data is None:  
      #If list is empty, both head and tail would point to new node.  
      self.head = newNode;  
      self.tail = newNode;  
      newNode.next = self.head;  
    else:  
        #Store data into temporary node  
        temp = self.head;  
        #New node will point to temp as next node  
        newNode.next = temp;  
        #New node will be the head node  
        self.head = newNode;  
        #Since, it is circular linked list tail will point to head.  
        self.tail.next = self.head;  
   
  #Displays all the nodes in the list  
  def display(self):  
    current = self.head;  
    if self.head is None:  
      print("List is empty");  
      return;  
    else:  
        print("Adding nodes to the start of the list: ");  
        #Prints each node by incrementing pointer.  
        print(current.data),  
        while(current.next != self.head):  
            current = current.next;  
            print(current.data),  
        print("\n");  
   
class CircularLinkedList:  
  cl = CreateList();  
    
  #Adding 1 to the list  
  cl.addAtStart(1);  
  cl.display();  
  #Adding 2 to the list  
  cl.addAtStart(2);  
  cl.display();  
  #Adding 3 to the list  
  cl.addAtStart(3);  
  cl.display();  
  #Adding 4 to the list  
  cl.addAtStart(4);  
  cl.display();  

Output:

Adding nodes to the start of the list: 
1
Adding nodes to the start of the list: 
2 1
Adding nodes to the start of the list: 
3 2 1
Adding nodes to the start of the list: 
4 3 2 1

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