Delete Node at Beginning in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output after deleting the first node in a singly linked list

What will be the printed linked list after deleting the first node?

DSA C

#include <stdio.h>
#include <stdlib.h>

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

void printList(struct Node* head) {
    while (head != NULL) {
        printf("%d -> ", head->data);
        head = head->next;
    }
    printf("NULL\n");
}

struct Node* deleteAtBeginning(struct Node* head) {
    if (head == NULL) return NULL;
    struct Node* temp = head;
    head = head->next;
    free(temp);
    return head;
}

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

    head->data = 10;
    head->next = second;
    second->data = 20;
    second->next = third;
    third->data = 30;
    third->next = NULL;

    head = deleteAtBeginning(head);
    printList(head);
    return 0;
}

A 20 -> 30 -> NULL

B 10 -> 20 -> 30 -> NULL

C 30 -> NULL

D NULL

💡 Hint

Deleting the first node means the head moves to the next node.

The function deleteAtBeginning removes the first node (which has data 10) and returns the new head pointing to the second node. So the list starts from 20 now.

🧠 Conceptual

intermediate

Effect of deleting the first node on list length

If a singly linked list has 5 nodes, how many nodes remain after deleting the first node?

A 3

B 5

C 0

D 4

💡 Hint

Deleting one node reduces the count by one.

Deleting the first node removes exactly one node from the list, so 5 - 1 = 4 nodes remain.

🔧 Debug

advanced

Identify the error in deleting the first node

What error will occur when running this code snippet to delete the first node?

DSA C

#include <stdio.h>
#include <stdlib.h>

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

struct Node* deleteAtBeginning(struct Node* head) {
    struct Node* temp = head;
    head = head->next;
    free(temp);
    return head;
}

int main() {
    struct Node* head = NULL;
    head = deleteAtBeginning(head);
    return 0;
}

A Segmentation fault (accessing NULL pointer)

B No error, runs fine

C Memory leak

D Compilation error

💡 Hint

Check what happens if head is NULL before accessing head->next.

The function does not check if head is NULL before accessing head->next. This causes a segmentation fault when head is NULL.

📝 Syntax

advanced

Correct syntax to delete the first node in a linked list

Which option correctly deletes the first node and updates the head pointer?

DSA C

struct Node* deleteAtBeginning(struct Node* head) {
    // Choose the correct implementation
}

A

struct Node* temp = head;
head = head->next;
free(temp);
return head;

B

if (head == NULL) return NULL;
struct Node* temp = head;
head = head->next;
free(temp);
return head;

C

if (head == NULL) return head;
free(head);
head = head->next;
return head;

D

if (head == NULL) return NULL;
free(head);
head = head->next;
return head;

💡 Hint

Always check if the list is empty before deleting.

Option B correctly checks if head is NULL before deleting. It saves the current head in temp, moves head to the next node, frees the old head, and returns the new head.

🚀 Application

expert

Resulting list after multiple deletions at beginning

Given a linked list with nodes 5 -> 10 -> 15 -> 20 -> NULL, what is the list after deleting the first node twice?

A 10 -> 15 -> 20 -> NULL

B 20 -> NULL

C 15 -> 20 -> NULL

D 5 -> 10 -> 15 -> 20 -> NULL

💡 Hint

Each deletion removes the current head node.

First deletion removes 5, list becomes 10 -> 15 -> 20 -> NULL.
Second deletion removes 10, list becomes 15 -> 20 -> NULL.