Delete a Node from Circular Linked List in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output after deleting a node from circular linked list

What is the printed state of the circular linked list after deleting the node with value 3?

DSA C

/* Circular linked list node structure */
#include <stdio.h>
#include <stdlib.h>

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

/* Function to print circular linked list */
void printList(Node* head) {
    if (!head) return;
    Node* temp = head;
    do {
        printf("%d -> ", temp->data);
        temp = temp->next;
    } while (temp != head);
    printf("null\n");
}

/* Function to delete node with given key */
Node* deleteNode(Node* head, int key) {
    if (!head) return NULL;
    Node *curr = head, *prev = NULL;
    
    // If head is to be deleted and only one node
    if (head->data == key && head->next == head) {
        free(head);
        return NULL;
    }

    // Find the node to delete
    do {
        if (curr->data == key) {
            if (prev) {
                prev->next = curr->next;
                if (curr == head) head = curr->next;
                free(curr);
                return head;
            } else {
                // Deleting head node
                Node* last = head;
                while (last->next != head) last = last->next;
                last->next = head->next;
                Node* temp = head;
                head = head->next;
                free(temp);
                return head;
            }
        }
        prev = curr;
        curr = curr->next;
    } while (curr != head);

    return head; // Key not found
}

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

    head->data = 1; head->next = second;
    second->data = 2; second->next = third;
    third->data = 3; third->next = fourth;
    fourth->data = 4; fourth->next = head;

    head = deleteNode(head, 3);
    printList(head);
    return 0;
}

A 1 -> 2 -> 4 -> null

B 1 -> 2 -> 3 -> 4 -> null

C 2 -> 3 -> 4 -> null

D 1 -> 4 -> null

💡 Hint

Remember that deleting a node removes it and links its previous node to the next node.

The node with value 3 is removed. The list links 2 directly to 4, so the printed list is 1 -> 2 -> 4 -> null.

❓ Predict Output

intermediate

Output after deleting the head node in circular linked list

What is the printed state of the circular linked list after deleting the node with value 1 (head node)?

DSA C

/* Same node structure and functions as before */

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

    head->data = 1; head->next = second;
    second->data = 2; second->next = third;
    third->data = 3; third->next = head;

    head = deleteNode(head, 1);
    printList(head);
    return 0;
}

A 3 -> 2 -> null

B 1 -> 2 -> 3 -> null

C 2 -> 3 -> null

D 2 -> null

💡 Hint

Deleting the head node means the new head is the next node.

The head node with value 1 is deleted. The last node (3) points to the new head (2). The printed list is 2 -> 3 -> null.

❓ Predict Output

advanced

Output after deleting the only node in circular linked list

What is the output after deleting the only node (value 10) in a circular linked list?

DSA C

/* Node structure and functions as before */

int main() {
    Node* head = malloc(sizeof(Node));
    head->data = 10;
    head->next = head;

    head = deleteNode(head, 10);
    if (!head) printf("List is empty\n");
    else printList(head);
    return 0;
}

A 10 -> null

B 10 -> 10 -> null

C null

D List is empty

💡 Hint

Deleting the only node should leave the list empty.

After deleting the only node, the list becomes empty (head is NULL). The program prints 'List is empty'.

❓ Predict Output

advanced

Output after deleting a non-existent node

What is the printed state of the circular linked list after trying to delete a node with value 5 which does not exist?

DSA C

/* Node structure and functions as before */

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

    head->data = 1; head->next = second;
    second->data = 2; second->next = third;
    third->data = 3; third->next = head;

    head = deleteNode(head, 5);
    printList(head);
    return 0;
}

A 1 -> 2 -> 3 -> null

B 2 -> 3 -> null

C null

D 1 -> 3 -> null

💡 Hint

If the node to delete is not found, the list remains unchanged.

Since node with value 5 does not exist, the list remains unchanged and prints 1 -> 2 -> 3 -> null.

🧠 Conceptual

expert

Why is it necessary to update the last node's next pointer when deleting the head in a circular linked list?

Choose the best explanation for why the last node's next pointer must be updated when deleting the head node in a circular linked list.

A Because the last node's next pointer points to NULL and must be changed to avoid a broken list.

B Because the last node's next pointer always points to the head, so it must point to the new head after deletion to maintain the circular structure.

C Because the last node's next pointer points to the node after the head, so it must be updated to point to the head again.

D Because the last node's next pointer is irrelevant and does not affect the list structure.

💡 Hint

Think about what keeps the circular linked list connected in a loop.

In a circular linked list, the last node's next pointer points to the head node. When the head is deleted, this pointer must be updated to point to the new head to keep the list circular.