Insertion at the beginning in circular linked list (original) (raw)

Last Updated : 30 Aug, 2025

Given a Circular Linked List and an integer key representing a node. Insert the given key node at the beginning of the circular linked list.

**Input: key = 5

**Output: 5 -> 1 -> 7 -> 8 -> 10
**Explanation: After inserting 5 at the beginning of the given circular linked list, it has elements as 5, 1, 7, 8, 10.

**Input: key = 1

**Output: 1 -> 2 -> 5 -> 7 -> 8 -> 10
**Explanation: After inserting 1 at the beginning of the given circular linked list, it has elements as 1, 2, 5, 7, 8, 10.

Try It Yourself

Insertion at the beginning in circular linked list

To insert a new node at the beginning of a circular linked list, we first create the **new node and allocate memory for it. If the list is empty (indicated by the last pointer being **NULL), we make the **new node point to itself. If the list already contains nodes then we set the **new node’s next pointer to point to the **current head of the list (which is **last->next), and then update the last node’s next pointer to point to the **new node. This maintains the circular structure of the list.

Step-by-step approach:

• Create a new node with the given value.
• Check Empty List (**last == **nullptr):
  • Make **newNode->next point to itself.
• Insert at Beginning:
  • Set **newNode->next to **last->next.
  • Update last->next to **newNode.

Below is the implementation of the above approach:

C++ `

#include using namespace std;

class Node { public: int data; Node* next;

Node(int x) {
    data = x;
    next = nullptr;
}

};

Node* insertAtBeginning(Node* last, int key) { Node* newNode = new Node(key);

if (last == nullptr) {
    newNode->next = newNode;
    return newNode;
}

newNode->next = last->next;
last->next = newNode;

return last;

}

void printList(Node* last) { if (last == nullptr) return;

Node* head = last->next;
Node* temp = head;

do {
    cout << temp->data;
    temp = temp->next;
    if (temp != head) cout << " -> ";
} while (temp != head);

cout << endl;

}

int main() { // Create circular linked list: 2 -> 3 -> 4 Node* first = new Node(2); first->next = new Node(3); first->next->next = new Node(4);

Node* last = first->next->next;
last->next = first;

// Insert 5 at the beginning
last = insertAtBeginning(last, 5);

printList(last);

return 0;

}

Java

class Node { int data; Node next;

Node(int x) {
    data = x;
    next = null;
}

}

class GfG {

static Node insertAtBeginning(Node last, int key) {
    Node newNode = new Node(key);

    if (last == null) {
        newNode.next = newNode;
        return newNode;
    }

    newNode.next = last.next;
    last.next = newNode;

    return last;
}

static void printList(Node last) {
    if (last == null) return;

    Node head = last.next;
    Node temp = head;

    do {
        System.out.print(temp.data);
        temp = temp.next;
        if (temp != head) System.out.print(" -> ");
    } while (temp != head);

    System.out.println();
}

public static void main(String[] args) {
    // Create circular linked list: 2 -> 3 -> 4
    Node first = new Node(2);
    first.next = new Node(3);
    first.next.next = new Node(4);

    Node last = first.next.next;
    last.next = first;

    // Insert 5 at the beginning
    last = insertAtBeginning(last, 5);

    printList(last);
}

}

Python

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

def insertAtBeginning(last, key): newNode = Node(key)

if last is None:
    newNode.next = newNode
    return newNode

newNode.next = last.next
last.next = newNode

return last

def printList(last): if last is None: return

head = last.next
temp = head

while True:
    print(temp.data, end="")
    temp = temp.next
    if temp != head:
        print(" -> ", end="")
    else:
        break
print()

if name == "main": # Create circular linked list: 2 -> 3 -> 4 first = Node(2) first.next = Node(3) first.next.next = Node(4)

last = first.next.next
last.next = first

# Insert 5 at the beginning
last = insertAtBeginning(last, 5)

printList(last)

C#

using System;

class Node { public int data; public Node next;

public Node(int x) {
    data = x;
    next = null;
}

}

class GfG { public static Node insertAtBeginning(Node last, int key) { Node newNode = new Node(key);

    if (last == null) {
        newNode.next = newNode;
        return newNode;
    }

    newNode.next = last.next;
    last.next = newNode;

    return last;
}

public static void printList(Node last) {
    if (last == null) return;

    Node head = last.next;
    Node temp = head;

    while (true) {
        Console.Write(temp.data);
        temp = temp.next;
        if (temp != head) {
            Console.Write(" -> ");
        } else {
            break;
        }
    }
    Console.WriteLine();
}

static void Main(string[] args) {
    // Create circular linked list: 2 -> 3 -> 4
    Node first = new Node(2);
    first.next = new Node(3);
    first.next.next = new Node(4);

    Node last = first.next.next;
    last.next = first;

    // Insert 5 at the beginning
    last = insertAtBeginning(last, 5);

    printList(last);
}

}

JavaScript

class Node { constructor(x) { this.data = x; this.next = null; } }

// Function to insert at beginning of circular linked list function insertAtBeginning(last, key) { let newNode = new Node(key);

if (last === null) {
    newNode.next = newNode;
    return newNode;
}

newNode.next = last.next;
last.next = newNode;

return last;

}

// Function to print circular linked list function printList(last) { if (last === null) return;

let head = last.next;
let temp = head;

while (true) {
    process.stdout.write(temp.data.toString());
    temp = temp.next;
    if (temp !== head) {
        process.stdout.write(" -> ");
    } else {
        break;
    }
}
console.log();

}

// Driver code let first = new Node(2); first.next = new Node(3); first.next.next = new Node(4);

let last = first.next.next; last.next = first;

// Insert 5 at beginning last = insertAtBeginning(last, 5);

printList(last);

`

**Time Complexity: O(1)
**Auxiliary Space: O(1)