Delete a Node from Circular Linked List in DSA C - Build from Scratch

Delete a Node from Circular Linked List

📖 Scenario: You are managing a circular linked list that represents a round-robin schedule of tasks. Each node contains a task ID. You need to remove a specific task from this circular list when it is completed.

🎯 Goal: Build a C program that creates a circular linked list with given task IDs, sets a target task ID to delete, deletes the node with that task ID from the circular linked list, and prints the resulting list.

📋 What You'll Learn

Create a circular linked list with exact task IDs: 10, 20, 30, 40, 50

Create an integer variable target with value 30

Write a function deleteNode that deletes the node with value target from the circular linked list

Print the circular linked list after deletion in the format: 10 -> 20 -> 40 -> 50 -> (back to head)

💡 Why This Matters

🌍 Real World

Circular linked lists are used in real-world applications like task scheduling, multiplayer games turn management, and buffering data streams where the list cycles continuously.

💼 Career

Understanding circular linked lists and node deletion is important for software engineers working on systems programming, embedded systems, and performance-critical applications.

1

Create the Circular Linked List

Define a struct Node with an integer data and a pointer next. Create five nodes with data 10, 20, 30, 40, and 50. Link them in a circular way so that the last node points back to the first node. Store the head pointer in head.

DSA C

// Define struct Node and create circular linked list with nodes 10, 20, 30, 40, 50
// Your code here

Hint

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

2

Set the Target Node to Delete

Create an integer variable called target and set it to 30. This is the value of the node you want to delete from the circular linked list.

DSA C

#include 
#include 

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

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

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

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

    third->data = 30;
    third->next = fourth;

    fourth->data = 40;
    fourth->next = fifth;

    fifth->data = 50;
    fifth->next = head; // circular link

    // Create an integer variable called target and set it to 30
    // Your code here

    return 0;
}

Hint

Just declare an integer variable named target and assign it the value 30.

3

Write the Function to Delete the Target Node

Write a function called deleteNode that takes two arguments: a pointer to the head node Node* head and an integer target. The function should delete the node with data equal to target from the circular linked list and return the new head pointer. Use this function in main to delete the node with value target.

DSA C

#include 
#include 

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

Node* deleteNode(Node* head, int target) {
    // Your code here
}

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

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

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

    third->data = 30;
    third->next = fourth;

    fourth->data = 40;
    fourth->next = fifth;

    fifth->data = 50;
    fifth->next = head; // circular link

    int target = 30;

    head = deleteNode(head, target);

    return 0;
}

Hint

Handle deleting the head node separately. For other nodes, traverse the list to find the target and remove it by adjusting pointers.

4

Print the Circular Linked List After Deletion

Write a loop to print the circular linked list starting from head. Print each node's data followed by ->. After printing all nodes, print (back to head) to show the circular nature.

DSA C

#include 
#include 

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

Node* deleteNode(Node* head, int target) {
    if (head == NULL) return NULL;

    Node *curr = head, *prev = NULL;

    if (head->data == target && head->next == head) {
        free(head);
        return NULL;
    }

    if (head->data == target) {
        Node* last = head;
        while (last->next != head) {
            last = last->next;
        }
        Node* temp = head;
        last->next = head->next;
        head = head->next;
        free(temp);
        return head;
    }

    prev = head;
    curr = head->next;
    while (curr != head) {
        if (curr->data == target) {
            prev->next = curr->next;
            free(curr);
            return head;
        }
        prev = curr;
        curr = curr->next;
    }

    return head;
}

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

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

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

    third->data = 30;
    third->next = fourth;

    fourth->data = 40;
    fourth->next = fifth;

    fifth->data = 50;
    fifth->next = head; // circular link

    int target = 30;

    head = deleteNode(head, target);

    // Print the circular linked list starting from head
    // Your code here

    return 0;
}

Hint

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

Practice

1. What happens when you delete the only node in a circular linked list?

easy

A. The list becomes empty (head = NULL)

B. The list still contains one node pointing to itself

C. The list becomes a linear linked list

D. The list throws an error

Solution

1. Step 1: Understand the structure of a single-node circular linked list

   It has one node whose next pointer points to itself.

2. Step 2: Delete the only node

   After deletion, no nodes remain, so the head pointer must be set to NULL to indicate an empty list.

3. Final Answer:

   The list becomes empty (head = NULL) -> Option A

4. Quick Check:

   Single node deleted means empty list [OK]

Hint: Deleting last node empties list, set head to NULL [OK]

Common Mistakes:

• Not setting head to NULL after deleting the only node
• Assuming list still has one node after deletion
• Confusing circular list with linear list after deletion

2. Which of the following is the correct syntax to delete the head node in a circular linked list in C?

easy

A. head = NULL; free(head);

B. head->next = NULL; free(head);

C. free(head); head = NULL;

D. Node* oldHead = head; head = head->next; free(oldHead);

Solution

1. Step 1: Understand deletion of head node in circular linked list

   We must move head pointer to next node and free the old head node.

2. Step 2: Check syntax correctness

   Node* oldHead = head; head = head->next; free(oldHead); correctly assigns head to head->next and frees the old head pointer stored separately.

3. Final Answer:

   Node* oldHead = head; head = head->next; free(oldHead); -> Option D

4. Quick Check:

   Move head, free old node [OK]

Hint: Move head to next, then free old head [OK]

Common Mistakes:

• Freeing head before moving pointer
• Setting next pointer to NULL breaks circular link
• Freeing NULL pointer

3. Given the circular linked list: 10 -> 20 -> 30 -> (back to 10), what is the list after deleting node with value 20?

medium

A. 10 -> 20 -> 30 -> (back to 10)

B. 20 -> 30 -> (back to 20)

C. 10 -> 30 -> (back to 10)

D. 30 -> 10 -> (back to 30)

Solution

1. Step 1: Identify node to delete and its neighbors

   Node with value 20 is between 10 and 30.

2. Step 2: Adjust pointers to remove node 20

   Set 10's next pointer to 30, skipping 20, maintaining circular link.

3. Final Answer:

   10 -> 30 -> (back to 10) -> Option C

4. Quick Check:

   Removed 20, linked 10 to 30 [OK]

Hint: Link previous node to next of deleted node [OK]

Common Mistakes:

• Not updating previous node's next pointer
• Breaking circular link by setting next to NULL
• Deleting wrong node

4. What is wrong with this code snippet for deleting a node with value 15 from a circular linked list?

void deleteNode(Node** head, int key) {
  Node* curr = *head;
  Node* prev = NULL;
  while (curr->data != key) {
    prev = curr;
    curr = curr->next;
  }
  prev->next = curr->next;
  free(curr);
}

medium

A. It does not handle deleting the head node correctly

B. It frees the wrong node

C. It causes infinite loop always

D. It sets head to NULL incorrectly

Solution

1. Step 1: Analyze deletion logic for head node

   If the node to delete is head, prev is NULL, so prev->next causes error.

2. Step 2: Identify missing head update

   Code does not update *head when deleting head node, causing incorrect list state.

3. Final Answer:

   It does not handle deleting the head node correctly -> Option A

4. Quick Check:

   Head deletion needs special handling [OK]

Hint: Check if node to delete is head before pointer update [OK]

Common Mistakes:

• Not updating head pointer when deleting head
• Dereferencing NULL prev pointer
• Not checking if node exists before deletion

5. You have a circular linked list with nodes: 5 -> 10 -> 15 -> 20 -> (back to 5). You want to delete the node with value 5 (head node). Which steps correctly delete the head and maintain the circular list?

hard

A. Set head to head->next, free old head, leave last node's next unchanged

B. Find last node, set its next to head->next, free head, update head to head->next

C. Free head, set head to NULL, list becomes empty

D. Set head->next to NULL, free head, update head to next node

Solution

1. Step 1: Locate last node in circular list

   Traverse nodes until node whose next points to head is found (node with value 20).

2. Step 2: Update last node's next pointer and head

   Set last node's next to head->next (node with value 10), free old head, and update head pointer to head->next.

3. Final Answer:

   Find last node, set its next to head->next, free head, update head to head->next -> Option B

4. Quick Check:

   Last node points to new head after deletion [OK]

Hint: Update last node's next before freeing head [OK]

Common Mistakes:

• Not updating last node's next pointer
• Freeing head before updating pointers
• Breaking circular link by setting next to NULL