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

When it is required to insert a new node at the beginning of a circular linked list, a 'Node' class needs to be created. In this class, there are two attributes, the data that is present in the node, and the access to the next node of the linked list.

In a circular linked list, the head and the rear are adjacent to each other. They are connected to form a circle, and don't have 'NULL' value in the last node. Instead, the last node points back to the first node.

Node Class Structure

First, we create a Node class to represent individual elements ?

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

Circular Linked List Implementation

The main class handles the circular linked list operations ?

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class CircularLinkedList:
    def __init__(self):
        self.head = None
        self.tail = None

    def add_at_beginning(self, data):
        new_node = Node(data)
        
        if self.head is None:
            # First node in the list
            self.head = new_node
            self.tail = new_node
            new_node.next = self.head
        else:
            # Insert at beginning
            new_node.next = self.head
            self.head = new_node
            self.tail.next = self.head

    def display(self):
        if self.head is None:
            print("The list is empty")
            return
        
        current = self.head
        result = []
        
        while True:
            result.append(str(current.data))
            current = current.next
            if current == self.head:
                break
        
        print(" -> ".join(result))

# Example usage
cll = CircularLinkedList()
print("Adding values to the circular linked list:")

cll.add_at_beginning(21)
cll.display()

cll.add_at_beginning(53)
cll.display()

cll.add_at_beginning(76)
cll.display()

Adding values to the circular linked list:
21
53 -> 21
76 -> 53 -> 21

How It Works

The add_at_beginning() method works in two scenarios:

• Empty list: The new node becomes both head and tail, pointing to itself
• Non-empty list: The new node points to the current head, becomes the new head, and the tail is updated to point to the new head

Visual Representation

Key Points

• The tail always points to the head in a circular linked list
• When inserting at the beginning, update both head and tail references
• The first node insertion creates a self-referencing loop
• Time complexity is O(1) for insertion at the beginning

Conclusion

Inserting at the beginning of a circular linked list requires careful handling of head and tail pointers. The key is maintaining the circular connection where the tail always points back to the head, ensuring the circular structure is preserved.