Insert at Beginning of Circular Linked List in DSA C - Build from Scratch

Insert at Beginning of Circular Linked List

📖 Scenario: You are managing a circular linked list that represents a playlist of songs. Each node contains the song's ID. You want to add a new song at the beginning of the playlist so it plays next.

🎯 Goal: Build a program in C that creates a circular linked list, then inserts a new node at the beginning, and finally prints the updated list.

📋 What You'll Learn

Define a struct Node with an int data and a struct Node* next pointer.

Create a circular linked list with three nodes having data 10, 20, and 30.

Add a function to insert a new node with data 5 at the beginning of the circular linked list.

Print the circular linked list starting from the head node after insertion.

💡 Why This Matters

🌍 Real World

Circular linked lists are used in applications like music playlists, round-robin scheduling, and buffering where the list loops back to the start.

💼 Career

Understanding circular linked lists helps in system programming, embedded systems, and designing efficient data structures for real-time applications.

1

Create the initial circular linked list

Define a struct Node with int data and struct Node* next. Then create three nodes with data 10, 20, and 30 linked in a circular way. Store the head pointer in head.

DSA C

# Define struct Node and create circular linked list with nodes 10, 20, 30
// Your code here

Hint

Remember to link the last node's next pointer back to head to make the list circular.

2

Add a function to insert at the beginning

Write a function called insertAtBeginning that takes struct Node** head and int data as parameters. This function should create a new node with the given data and insert it at the beginning of the circular linked list, updating the head pointer.

DSA C

#include 
#include 

struct Node {
    int data;
    struct Node* next;
};

// Write insertAtBeginning function here
// Your code here

int main() {
    struct Node* head = (struct Node*)malloc(sizeof(struct Node));
    struct Node* second = (struct Node*)malloc(sizeof(struct Node));
    struct Node* third = (struct Node*)malloc(sizeof(struct Node));

    head->data = 10;
    head->next = second;

    second->data = 20;
    second->next = third;

    third->data = 30;
    third->next = head; // circular link

    return 0;
}

Hint

To insert at the beginning, find the last node to update its next pointer to the new node, then update head.

3

Call the insert function to add new node

In main, call insertAtBeginning with &head and 5 to insert a new node with data 5 at the beginning of the circular linked list.

DSA C

#include 
#include 

struct Node {
    int data;
    struct Node* next;
};

void insertAtBeginning(struct Node** head, int data) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = data;

    if (*head == NULL) {
        newNode->next = newNode;
        *head = newNode;
        return;
    }

    struct Node* temp = *head;
    while (temp->next != *head) {
        temp = temp->next;
    }

    newNode->next = *head;
    temp->next = newNode;
    *head = newNode;
}

int main() {
    struct Node* head = (struct Node*)malloc(sizeof(struct Node));
    struct Node* second = (struct Node*)malloc(sizeof(struct Node));
    struct Node* third = (struct Node*)malloc(sizeof(struct Node));

    head->data = 10;
    head->next = second;

    second->data = 20;
    second->next = third;

    third->data = 30;
    third->next = head; // circular link

    // Call insertAtBeginning to add node with data 5
    // Your code here

    return 0;
}

Hint

Call insertAtBeginning with the address of head and the value 5.

4

Print the circular linked list

Write a function called printList that takes struct Node* head and prints the data of each node in the circular linked list separated by ->. Then call printList(head) in main after insertion.

DSA C

#include 
#include 

struct Node {
    int data;
    struct Node* next;
};

void insertAtBeginning(struct Node** head, int data) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = data;

    if (*head == NULL) {
        newNode->next = newNode;
        *head = newNode;
        return;
    }

    struct Node* temp = *head;
    while (temp->next != *head) {
        temp = temp->next;
    }

    newNode->next = *head;
    temp->next = newNode;
    *head = newNode;
}

// Write printList function here
// Your code here

int main() {
    struct Node* head = (struct Node*)malloc(sizeof(struct Node));
    struct Node* second = (struct Node*)malloc(sizeof(struct Node));
    struct Node* third = (struct Node*)malloc(sizeof(struct Node));

    head->data = 10;
    head->next = second;

    second->data = 20;
    second->next = third;

    third->data = 30;
    third->next = head; // circular link

    insertAtBeginning(&head, 5);

    // Call printList to display the list
    // Your code here

    return 0;
}

Hint

Use a do-while loop to print nodes until you reach the head again.