In computer science, circular linked lists are an elegant data structure where the last node in the list points back to the first node, forming a closed loop. These structures are commonly used in systems requiring round-robin scheduling, buffered data streams, and certain types of games or applications. A particularly interesting operation in a circular linked list is insertion at a specific position.
In this detailed explanation, we will break down the entire process step-by-step, ensuring a thorough understanding of how this operation is executed.
Table of Contents

Overview of Circular Linked Lists
A circular linked list differs from a traditional linked list in that it does not terminate at the last node. Instead, the last node contains a reference to the first node, creating a cyclic structure. This property ensures that traversal can continue indefinitely unless explicitly stopped. There are two primary types of circular linked lists:
- Singly Circular Linked List (SCLL): Each node has one pointer, which points to the next node in the sequence.
- Doubly Circular Linked List (DCLL): Each node contains two pointers: one pointing to the next node and the other pointing to the previous node.
For this post, we focus on the singly circular linked list, which is the simpler and more commonly used version.
Steps to Insert at a Specific Position
The insertion operation in a circular linked list involves updating the pointers of existing nodes to accommodate the new node, ensuring the circular structure remains intact. Let’s explore each step in detail.

1. Check if the List is Empty
Before attempting any insertion, we first determine if the list is empty. A circular linked list is considered empty if its head pointer is NULL
.
- Case 1: Position is not 1
If the desired position for insertion is not 1, we cannot proceed because the list lacks nodes. Attempting to access a non-existent position would result in an error. In such cases, an appropriate error message is displayed, indicating that the insertion cannot be performed. - Case 2: Position is 1
If the position is 1, we proceed by creating a new node. Since this new node will be the only element in the list, it will point to itself, maintaining the circular structure. The head pointer is updated to reference this new node.
2. Create the New Node
Regardless of whether the list is empty or not, a new node is created using a predefined Node structure or class. In most programming languages, this involves allocating memory for the node and initializing its data field with the given value. The next pointer is initially set to NULL
and will be updated later during insertion.
3. Traverse the List to Find the Insertion Point
When inserting a node at a specific position other than 1, we need to locate the node currently occupying that position or its preceding node. Traversal in a circular linked list is done using a temporary pointer (temp
) initialized to the head node.
- Start from the head node and iterate through the list while maintaining a counter.
- Stop when the counter matches the desired position minus one (for inserting in the middle or end) or when the next pointer points back to the head (indicating the end of the list has been reached).
If the position is greater than the number of nodes in the list, the insertion cannot be performed, and an appropriate error message is displayed.
4. Handle Special Case: Insertion at Position 1
When inserting at position 1 in a non-empty list, the new node becomes the first node. Here’s how we achieve this:
- Set the next pointer of the new node to the current head.
- Traverse the list to locate the last node, which points back to the head.
- Update the next pointer of the last node to reference the new node.
- Update the head pointer to point to the new node.
This ensures that the circular structure is preserved while the new node takes its place at the beginning of the list.
5. Update Pointers for Middle or End Insertion
For positions other than 1, we adjust the next pointers of the relevant nodes:
- Traverse the list to find the node immediately preceding the desired position (
prev
). - Set the next pointer of the new node to reference the node currently at the desired position.
- Update the next pointer of the preceding node to point to the new node.
If the new node is being inserted at the end of the list, we also update the last pointer (if applicable) to reference the new node. This step ensures that the list remains circular, with the last node pointing back to the head.
Maintaining Circular Structure
The key to successful insertion lies in preserving the circular nature of the list. Any disruption in the pointer adjustments could break the loop, converting the list into a traditional singly linked list or creating an inaccessible segment of nodes. Hence, careful attention must be given to pointer updates during insertion, particularly for edge cases such as inserting at the first or last positions.
Implementation of Code in Multiple Programming Languages

C Implementation
#include <stdio.h>
#include <stdlib.h>
// Define the Node structure
struct Node {
int data;
struct Node* next;
};
// Function to create a new node
struct Node* createNode(int value) {
struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = value;
newNode->next = NULL;
return newNode;
}
// Function to insert a node at a specific position in a circular linked list
struct Node* insertAtPosition(struct Node* last, int data, int pos) {
if (last == NULL) {
// If the list is empty
if (pos != 1) {
printf("Invalid position!\n");
return last;
}
// Create a new node and make it point to itself
struct Node* newNode = createNode(data);
last = newNode;
last->next = last;
return last;
}
// Create a new node with the given data
struct Node* newNode = createNode(data);
struct Node* curr = last->next;
if (pos == 1) {
// Insert at the beginning
newNode->next = curr;
last->next = newNode;
return last;
}
// Traverse the list to find the insertion point
for (int i = 1; i < pos - 1; ++i) {
curr = curr->next;
if (curr == last->next) {
printf("Invalid position!\n");
return last;
}
}
// Insert the new node at the desired position
newNode->next = curr->next;
curr->next = newNode;
// Update last if the new node is inserted at the end
if (curr == last) {
last = newNode;
}
return last;
}
// Function to print the circular linked list
void printList(struct Node* last) {
if (last == NULL) {
printf("List is empty.\n");
return;
}
struct Node* head = last->next;
do {
printf("%d ", head->data);
head = head->next;
} while (head != last->next);
printf("\n");
}
int main() {
// Create circular linked list: 2 -> 3 -> 4 -> (back to 2)
struct Node* first = createNode(2);
first->next = createNode(3);
first->next->next = createNode(4);
struct Node* last = first->next->next;
last->next = first; // Completing the circular link
printf("Original list: ");
printList(last);
// Insert elements at specific positions
int data = 5, pos = 2;
last = insertAtPosition(last, data, pos);
printf("List after insertions: ");
printList(last);
return 0;
}
Explanation
- Node Creation (
createNode
): Dynamically allocates memory for a node, sets itsdata
, and initializes thenext
pointer toNULL
. - Insertion Logic (
insertAtPosition
):- Handles special cases like inserting into an empty list or inserting at the beginning.
- Traverses the circular list to find the correct position.
- Updates pointers to maintain the circular structure.
- Traversal (
printList
):- Starts from
last->next
(head of the list). - Traverses the list using a
do-while
loop to ensure all nodes are printed.
- Starts from
C++ Implementation
#include <iostream>
using namespace std;
// Define the Node structure
struct Node {
int data;
Node *next;
};
// Function to create a new node
Node* createNode(int value) {
Node* newNode = new Node();
newNode->data = value;
newNode->next = nullptr;
return newNode;
}
// Function to insert a node at a specific position in a circular linked list
Node* insertAtPosition(Node* last, int data, int pos) {
if (last == nullptr) {
if (pos != 1) {
cout << "Invalid position!" << endl;
return last;
}
Node* newNode = createNode(data);
last = newNode;
last->next = last;
return last;
}
Node* newNode = createNode(data);
Node* curr = last->next;
if (pos == 1) {
newNode->next = curr;
last->next = newNode;
return last;
}
for (int i = 1; i < pos - 1; ++i) {
curr = curr->next;
if (curr == last->next) {
cout << "Invalid position!" << endl;
return last;
}
}
newNode->next = curr->next;
curr->next = newNode;
if (curr == last) last = newNode;
return last;
}
// Function to print the circular linked list
void printList(Node* last) {
if (last == nullptr) return;
Node* head = last->next;
do {
cout << head->data << " ";
head = head->next;
} while (head != last->next);
cout << endl;
}
int main() {
Node* first = createNode(2);
first->next = createNode(3);
first->next->next = createNode(4);
Node* last = first->next->next;
last->next = first;
cout << "Original list: ";
printList(last);
int data = 5, pos = 2;
last = insertAtPosition(last, data, pos);
cout << "List after insertions: ";
printList(last);
return 0;
}
C# Implementation
using System;
class Node {
public int Data;
public Node Next;
public Node(int value) {
Data = value;
Next = null;
}
}
class CircularLinkedList {
public static Node InsertAtPosition(Node last, int data, int pos) {
if (last == null) {
if (pos != 1) {
Console.WriteLine("Invalid position!");
return last;
}
Node newNode = new Node(data);
last = newNode;
last.Next = last;
return last;
}
Node newNode = new Node(data);
Node curr = last.Next;
if (pos == 1) {
newNode.Next = curr;
last.Next = newNode;
return last;
}
for (int i = 1; i < pos - 1; ++i) {
curr = curr.Next;
if (curr == last.Next) {
Console.WriteLine("Invalid position!");
return last;
}
}
newNode.Next = curr.Next;
curr.Next = newNode;
if (curr == last) last = newNode;
return last;
}
public static void PrintList(Node last) {
if (last == null) return;
Node head = last.Next;
do {
Console.Write(head.Data + " ");
head = head.Next;
} while (head != last.Next);
Console.WriteLine();
}
public static void Main() {
Node first = new Node(2);
first.Next = new Node(3);
first.Next.Next = new Node(4);
Node last = first.Next.Next;
last.Next = first;
Console.WriteLine("Original list: ");
PrintList(last);
int data = 5, pos = 2;
last = InsertAtPosition(last, data, pos);
Console.WriteLine("List after insertions: ");
PrintList(last);
}
}
Java Implementation
class Node {
int data;
Node next;
Node(int value) {
data = value;
next = null;
}
}
public class CircularLinkedList {
static Node insertAtPosition(Node last, int data, int pos) {
if (last == null) {
if (pos != 1) {
System.out.println("Invalid position!");
return last;
}
Node newNode = new Node(data);
last = newNode;
last.next = last;
return last;
}
Node newNode = new Node(data);
Node curr = last.next;
if (pos == 1) {
newNode.next = curr;
last.next = newNode;
return last;
}
for (int i = 1; i < pos - 1; ++i) {
curr = curr.next;
if (curr == last.next) {
System.out.println("Invalid position!");
return last;
}
}
newNode.next = curr.next;
curr.next = newNode;
if (curr == last) last = newNode;
return last;
}
static void printList(Node last) {
if (last == null) return;
Node head = last.next;
do {
System.out.print(head.data + " ");
head = head.next;
} while (head != last.next);
System.out.println();
}
public static void main(String[] args) {
Node first = new Node(2);
first.next = new Node(3);
first.next.next = new Node(4);
Node last = first.next.next;
last.next = first;
System.out.println("Original list: ");
printList(last);
int data = 5, pos = 2;
last = insertAtPosition(last, data, pos);
System.out.println("List after insertions: ");
printList(last);
}
}
JavaScript Implementation
class Node {
constructor(value) {
this.data = value;
this.next = null;
}
}
function insertAtPosition(last, data, pos) {
if (!last) {
if (pos !== 1) {
console.log("Invalid position!");
return last;
}
const newNode = new Node(data);
last = newNode;
last.next = last;
return last;
}
const newNode = new Node(data);
let curr = last.next;
if (pos === 1) {
newNode.next = curr;
last.next = newNode;
return last;
}
for (let i = 1; i < pos - 1; ++i) {
curr = curr.next;
if (curr === last.next) {
console.log("Invalid position!");
return last;
}
}
newNode.next = curr.next;
curr.next = newNode;
if (curr === last) last = newNode;
return last;
}
function printList(last) {
if (!last) return;
let head = last.next;
do {
process.stdout.write(head.data + " ");
head = head.next;
} while (head !== last.next);
console.log();
}
const first = new Node(2);
first.next = new Node(3);
first.next.next = new Node(4);
let last = first.next.next;
last.next = first;
console.log("Original list: ");
printList(last);
const data = 5, pos = 2;
last = insertAtPosition(last, data, pos);
console.log("List after insertions: ");
printList(last);
Python Implementation
class Node:
def __init__(self, data):
self.data = data
self.next = None
def insert_at_position(last, data, pos):
if not last:
if pos != 1:
print("Invalid position!")
return last
new_node = Node(data)
last = new_node
last.next = last
return last
new_node = Node(data)
curr = last.next
if pos == 1:
new_node.next = curr
last.next = new_node
return last
for _ in range(1, pos - 1):
curr = curr.next
if curr == last.next:
print("Invalid position!")
return last
new_node.next = curr.next
curr.next = new_node
if curr == last:
last = new_node
return last
def print_list(last):
if not last:
return
head = last.next
while True:
print(head.data, end=" ")
head = head.next
if head == last.next:
break
print()
first = Node(2)
first.next = Node(3)
first.next.next = Node(4)
last = first.next.next
last.next = first
print("Original list: ")
print_list(last)
data, pos = 5, 2
last = insert_at_position(last, data, pos)
print("List after insertions: ")
print_list(last)
Expected Output
Original list: 2 3 4
List after insertions: 2 5 3 4
Output Explanation
Let’s break down the output for the provided implementations:
Input Details
- Original Circular Linked List:
2 -> 3 -> 4 -> (back to 2)
- Insert Data:
5
- Position:
2
Step-by-Step Output
- Original List:
- The circular linked list is printed starting from the node next to
last
:
- The circular linked list is printed starting from the node next to
Original list: 2 3 4
This is because the list is traversed starting from last->next
.
- Insertion at Position 2:
- A new node with data
5
is created. - The new node is inserted after the first node (
2
), and itsnext
pointer is updated to point to the second node (3
). - The
next
pointer of the first node (2
) is updated to point to the new node (5
). - The updated circular linked list is:
2 -> 5 -> 3 -> 4 -> (back to 2)
- A new node with data
- Updated List After Insertion:
- The circular linked list is printed again, starting from the node next to
last
:
- The circular linked list is printed again, starting from the node next to
List after insertions: 2 5 3 4
Time Complexity
The time complexity of inserting a node at a specific position in a circular linked list depends on the position at which the node is inserted.
- Best Case:
- If the position is
1
(inserting at the beginning), the time complexity is O(1) because it requires only a constant amount of operations to update pointers.
- If the position is
- Worst Case:
- If the position is at the end or out of bounds, the function traverses the entire list, leading to a time complexity of O(n), where
n
is the number of nodes in the list.
- If the position is at the end or out of bounds, the function traverses the entire list, leading to a time complexity of O(n), where
- Average Case:
- On average, the time complexity is O(n/2) (which simplifies to O(n)) since it may traverse half the list.
Auxiliary Space Complexity
The auxiliary space complexity is O(1) because the function only uses a constant amount of extra space for pointers like curr
and newNode
.
Summary
- Time Complexity:
- Best case: O(1)
- Worst case: O(n)
- Average case: O(n)
- Auxiliary Space Complexity: O(1)
Applications of Circular Linked Lists
Circular linked lists are widely used in scenarios where a looping structure is essential. Some common applications include:
- Operating Systems: Used in round-robin scheduling to allocate CPU time to processes.
- Data Streaming: Provides seamless buffering for continuous data flows.
- Simulations: Models scenarios where entities or objects cycle through states.
Advantages of Insertion at a Specific Position in a Circular Linked List
The ability to insert a new node at any position in a circular linked list provides flexibility and makes this data structure highly adaptable to various use cases. Let’s explore the key advantages of this operation in detail:
- Efficient Use of Memory
- Circular linked lists do not require a predefined size, as nodes are dynamically allocated memory when needed. The insertion operation, especially at a specific position, ensures that memory is utilized efficiently. Unlike arrays, there is no need to shift elements to accommodate a new entry, as only the pointers are updated.
- Maintaining the Circular Structure
- When inserting at a specific position, the circular nature of the list remains intact. This is especially beneficial in systems where continuity is essential, such as real-time applications or data streaming, where looping through the list is required without interruption or termination.
- Flexibility in Data Management
- Inserting a node at a specific position allows developers to organize data in the desired sequence. This flexibility is crucial for tasks like:
- Prioritizing certain elements by inserting them at the beginning.
- Balancing workloads by strategically inserting nodes in a round-robin schedule.
- Maintaining sorted order by placing elements at their correct positions.
- Inserting a node at a specific position allows developers to organize data in the desired sequence. This flexibility is crucial for tasks like:
- Fast Insertion at Specific Points
- While the traversal to the desired position may take linear time (O(n)O(n)), the actual insertion operation is swift. Once the target position is located, only a few pointer adjustments are needed, which is computationally efficient.
- Applicability in Continuous and Rotational Processes
- In circular linked lists, inserting at a specific position allows seamless integration of new elements in applications like:
- Multiplayer games: To add new players into an ongoing cycle of turns.
- Operating systems: To add a new process or task into a circular queue for scheduling.
- Traffic signal systems: Where new traffic lights can be inserted into the rotation.
- In circular linked lists, inserting at a specific position allows seamless integration of new elements in applications like:
- Dynamic Growth Without Fragmentation
- Unlike arrays, where resizing can lead to performance bottlenecks or memory fragmentation, circular linked lists grow dynamically as nodes are inserted. This ensures that the list remains contiguous and efficient, even as elements are added at various positions.
- Simplified Special Case Handling
- Circular linked lists handle special cases, such as inserting at the beginning or end, with minimal additional logic. For example:
- Insertion at the beginning: Adjusting the last node’s pointer ensures the circular structure remains intact.
- Insertion at the end: The same logic applies, as the end node automatically connects back to the head.
- This consistency simplifies the implementation compared to other data structures like doubly linked lists or arrays.
- Circular linked lists handle special cases, such as inserting at the beginning or end, with minimal additional logic. For example:
- Enhanced Traversal for Verification
- After insertion, verifying the success of the operation is straightforward due to the circular nature of the list. A simple traversal from the head ensures that all nodes, including the newly inserted one, can be accessed without missing any.
- Inserting a specific position in a circular linked list is a powerful feature that enhances the versatility and efficiency of this data structure. Whether it’s for dynamic data handling, continuous process management, or real-time applications, this operation ensures the smooth integration of new elements without disrupting the existing structure. This adaptability makes circular linked lists an invaluable tool in solving a wide range of computational problems.
By understanding and mastering the operation of inserting at a specific position, developers can leverage the full potential of circular linked lists in designing efficient and robust systems.
Related Articles
- Introduction to Circular Linked Lists: A Comprehensive Guide
- Understanding Circular Singly Linked Lists: A Comprehensive Guide
- Circular Doubly Linked List: A Comprehensive Guide
- Insertion in Circular Singly Linked List: A Comprehensive Guide
- Insertion in an Empty Circular Linked List: A Detailed Exploration
- Insertion at the Beginning in Circular Linked List: A Detailed Exploration
- Insertion at the End of a Circular Linked List: A Comprehensive Guide
- Insertion at a Specific Position in a Circular Linked List: A Detailed Exploration
- Deletion from a Circular Linked List: A Comprehensive Guide
- Deletion from the Beginning of a Circular Linked List: A Detailed Exploration
- Deletion at Specific Position in Circular Linked List: A Detailed Exploration
- Deletion at the End of a Circular Linked List: A Comprehensive Guide
- Searching in a Circular Linked List: A Comprehensive Exploration
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Frequently Asked Questions (FAQs) on Circular Linked Lists and Insertion at a Specific Position
What is a circular linked list, and how does it differ from a traditional linked list?
A circular linked list is a variation of the standard linked list where the last node’s pointer connects back to the first node, forming a closed loop. This differs from a singly linked list, where the last node’s pointer is NULL
, signifying the end of the list.
In a circular singly linked list (SCLL):
- Each node contains data and a next pointer.
- The next pointer of the last node points to the first node, ensuring continuity.
In contrast, in a doubly linked list or doubly circular linked list (DCLL):
- Each node has two pointers: next and prev.
- In the circular variation, the prev pointer of the first node points to the last node, and the next pointer of the last node points to the first node.
Advantages of a circular linked list over a traditional linked list include:
- No termination point: Traversal can continue indefinitely unless explicitly stopped.
- Efficient memory usage: Eliminates the need for a null termination marker, making the list structure more compact.
What are the advantages of inserting a node at a specific position in a circular linked list?
Inserting a node at a specific position in a circular linked list offers several benefits:
- Dynamic growth: Nodes can be inserted anywhere without resizing or shifting elements.
- Efficient memory usage: Since nodes are dynamically allocated, memory is utilized efficiently.
- Flexibility in organization: Allows prioritization or sorting of data by strategically placing nodes.
- Simplified edge case handling: Whether inserting at the beginning, middle, or end, the circular structure remains intact with minimal adjustments.
- Applicability in real-world problems: Useful in round-robin scheduling, continuous processes, or cyclic simulations.
How do you handle edge cases when inserting a node at position 1 in a circular linked list?
When inserting at position 1, special care is needed to ensure the circular structure is maintained:
- Create the new node and set its next pointer to the current head node.
- If the list is empty, make the new node point to itself and set it as the head node.
- Traverse the list to locate the last node (the node whose next pointer points back to the head).
- Update the next pointer of the last node to reference the new node.
- Update the head pointer to point to the new node.
This ensures that the new node becomes the first node, the previous head node moves to the second position, and the list remains circular.
What happens if you try to insert a node at a position that exceeds the length of the list?
In a circular linked list, attempting to insert a node at a position greater than the number of nodes plus one is invalid. For example:
- In a list with 3 nodes, positions 1 through 4 are valid (4 represents appending at the end).
- Positions greater than 4 are invalid.
When an invalid position is specified:
- Traversal stops prematurely: The pointer reaches the last node and loops back to the head.
- Error handling: The program typically returns an error message indicating an invalid position.
This ensures the list remains consistent and avoids undefined behavior.
Why is a circular linked list preferred for round-robin scheduling?
Round-robin scheduling is a time-sharing algorithm widely used in operating systems to allocate CPU time to processes. A circular linked list is ideal for this because:
- Cyclic nature: Processes are executed in a continuous loop without needing to restart traversal manually.
- Efficient insertion/deletion: New processes can be added or removed from the queue with minimal overhead.
- Fair distribution: All processes get an equal chance, as traversal always returns to the head after completing the last node.
For example, inserting a high-priority process at the beginning or a low-priority process at the end is straightforward with a circular linked list.
How is the last node identified in a circular linked list?
Identifying the last node is essential for operations like inserting a node at the end or the beginning. In a circular linked list:
- Start traversal from the head node.
- Continue iterating through the nodes using the next pointer.
- The node whose next pointer points back to the head is the last node.
This process ensures accurate updates to maintain the circular structure during insertion or deletion.
How does insertion at a specific position differ between singly and doubly circular linked lists?
In a singly circular linked list (SCLL):
- Each node contains only a next pointer.
- Insertion involves updating the next pointers of the preceding and new nodes.
- Traversal is unidirectional.
In a doubly circular linked list (DCLL):
- Each node contains both next and prev pointers.
- Insertion requires updating both pointers in the preceding and subsequent nodes, as well as the new node.
- Traversal can be done in either direction, making certain operations more efficient.
While DCLL provides greater flexibility, the additional pointer updates make insertion more complex than in SCLL.
What is the time complexity of inserting a node at a specific position in a circular linked list?
The time complexity of inserting a node at a specific position in a circular linked list is:
- Best case: O(1) if inserting at the beginning, as no traversal is required.
- Worst case: O(n), where n is the number of nodes, if inserting at the end or a middle position.
The traversal time depends on the position of insertion:
- For position 1, only pointer adjustments are made.
- For other positions, traversal up to the preceding node is required, resulting in linear time complexity.
What are some real-world applications of circular linked lists?
Circular linked lists have a wide range of real-world applications, including:
- Operating systems: Used in round-robin scheduling for CPU and I/O process management.
- Gaming applications: Managing player turns in multiplayer games.
- Data streams: Implementing circular buffers for continuous data flow.
- Traffic control systems: Rotational control of traffic signals.
- Audio and video streaming: Looping playback of media files.
Their cyclic structure makes them ideal for scenarios requiring continuous or repeated operations.
What are the drawbacks of circular linked lists compared to other data structures?
While circular linked lists are highly versatile, they have some limitations:
- Linear traversal: Accessing a specific node requires O(n) time, unlike arrays with O(1) direct access.
- Complexity in debugging: The circular nature can lead to infinite loops during traversal if termination conditions are not carefully implemented.
- Additional pointer management: Compared to arrays, managing pointers adds complexity, especially for doubly circular linked lists.
Despite these drawbacks, their advantages in certain use cases outweigh these limitations, making them a preferred choice for dynamic and cyclic data structures.