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.

Practice

1. What happens to the linked list when you delete the node at the beginning?

easy

A. All nodes are deleted at once.

B. The last node is deleted instead of the first.

C. The list remains unchanged.

D. The head pointer moves to the next node, removing the first node.

Solution

1. Step 1: Understand the head pointer role

   The head pointer points to the first node in the linked list.

2. Step 2: Effect of deleting the first node

   Deleting the first node means moving the head pointer to the second node, effectively removing the first node from the list.

3. Final Answer:

   The head pointer moves to the next node, removing the first node. -> Option D

4. Quick Check:

   Deleting at beginning means head moves forward [OK]

Hint: Deleting at start moves head to next node [OK]

Common Mistakes:

• Thinking the last node is deleted
• Assuming the list stays the same
• Deleting all nodes instead of one

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

easy

A. temp = head; head = head->next; free(temp);

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

C. free(head); head = head->next;

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

Solution

1. Step 1: Store current head in temp

   We save the current head node in a temporary pointer to free it later.

2. Step 2: Move head to next node and free old head

   Update head to point to the next node, then free the old head stored in temp.

3. Final Answer:

   temp = head; head = head->next; free(temp); -> Option A

4. Quick Check:

   Save old head, move head, free old [OK]

Hint: Save old head before moving and freeing [OK]

Common Mistakes:

• Freeing head before moving pointer
• Not saving old head before moving
• Setting next to NULL incorrectly

3. What will be the output linked list after deleting the first node from the list: 10 -> 20 -> 30 -> NULL?

medium

A. 10 -> 20 -> 30 -> NULL

B. NULL

C. 20 -> 30 -> NULL

D. 30 -> NULL

Solution

1. Step 1: Identify the first node

   The first node has value 10.

2. Step 2: Delete first node and move head

   After deletion, head points to node with value 20, so list starts from 20.

3. Final Answer:

   20 -> 30 -> NULL -> Option C

4. Quick Check:

   First node removed, next node becomes head [OK]

Hint: After deletion, list starts from second node [OK]

Common Mistakes:

• Not updating head pointer
• Deleting wrong node
• Assuming list becomes empty

4. Consider this code snippet to delete the first node:

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

What is the error in this code?

medium

A. It frees the new head instead of the old head.

B. It does not update the head pointer.

C. It frees the temp pointer instead of head.

D. It causes a syntax error.

Solution

1. Step 1: Analyze pointer usage

   temp stores old head, head moves to next node.

2. Step 2: Identify which node is freed

   free(head) frees the new head, not the old node stored in temp, causing memory error.

3. Final Answer:

   It frees the new head instead of the old head. -> Option A

4. Quick Check:

   Free old node, not new head [OK]

Hint: Free the saved old head pointer, not the updated head [OK]

Common Mistakes:

• Freeing updated head instead of old node
• Not freeing any node causing memory leak
• Confusing temp and head pointers

5. You have a singly linked list with nodes: 5 -> 15 -> 25 -> 35 -> NULL. After deleting the first node twice, what will be the resulting list?

hard

A. 15 -> 25 -> 35 -> NULL

B. 25 -> 35 -> NULL

C. 35 -> NULL

D. NULL

Solution

1. Step 1: Delete first node once

   First deletion removes 5, list becomes 15 -> 25 -> 35 -> NULL.

2. Step 2: Delete first node again

   Second deletion removes 15, list becomes 25 -> 35 -> NULL.

3. Final Answer:

   25 -> 35 -> NULL -> Option B

4. Quick Check:

   Two deletions remove first two nodes [OK]

Hint: Each deletion moves head forward by one node [OK]

Common Mistakes:

• Deleting only once instead of twice
• Confusing node values after deletion
• Assuming list becomes empty too soon