Delete Node at Beginning in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to delete the first node of a singly linked list.

DSA Java

public void deleteAtBeginning() {
    if (head == null) {
        return;
    }
    head = [1];
}

Drag options to blanks, or click blank then click option'

Ahead.next

Bhead

Cnull

Dhead.prev

Attempts:

3 left

💡 Hint

Common Mistakes

Setting head to null deletes the entire list.

Using head.prev is invalid in singly linked list.

To delete the first node, we move the head pointer to the next node.

2fill in blank

medium

Complete the code to print the linked list after deleting the first node.

DSA Java

public void printList() {
    Node current = head;
    while (current != [1]) {
        System.out.print(current.data + " -> ");
        current = current.next;
    }
    System.out.println("null");
}

Drag options to blanks, or click blank then click option'

Anull

Bhead

Ccurrent

Dhead.next

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of null causes infinite loop.

Using current instead of null causes infinite loop.

The loop should continue until current is null, which means end of list.

3fill in blank

hard

Fix the error in the deleteAtBeginning method to avoid NullPointerException.

DSA Java

public void deleteAtBeginning() {
    if (head == null) {
        return;
    }
    Node temp = head;
    head = head.next;
    [1] = null;
}

Drag options to blanks, or click blank then click option'

Anull

Btemp

Chead.prev

Dhead.next

Attempts:

3 left

💡 Hint

Common Mistakes

Setting head.next to null causes loss of list.

Setting null to null does nothing.

Setting the old head to null helps garbage collection and avoids dangling references.

4fill in blank

hard

Fill both blanks to complete the method that deletes the first node and returns its data.

DSA Java

public int deleteAtBeginning() {
    if (head == null) {
        return -1;
    }
    int data = head.data;
    Node temp = head;
    head = [1];
    [2] = null;
    return data;
}

Drag options to blanks, or click blank then click option'

Ahead.next

Bhead

Ctemp

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Setting head to null deletes entire list.

Not setting old node to null causes memory leaks.

Move head to next node, then set old head (temp) to null to delete it.

5fill in blank

hard

Fill all three blanks to implement a safe delete at beginning that handles empty list and returns deleted node data.

DSA Java

public Integer deleteAtBeginning() {
    if (head == [1]) {
        return [2];
    }
    int deletedData = head.data;
    Node oldHead = head;
    head = [3];
    oldHead = null;
    return deletedData;
}

Drag options to blanks, or click blank then click option'

Anull

B-1

Chead.next

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Returning null instead of -1 for empty list.

Not checking for empty list causes errors.

Check if head is null (empty list), return -1. Otherwise, move head to next node and delete old head.

Practice

1. What happens to the head pointer when you delete a node at the beginning of a singly linked list?

easy

A. It moves to the next node in the list

B. It becomes null immediately

C. It points to the last node

D. It remains unchanged

Solution

1. Step 1: Understand the head pointer role

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

2. Step 2: Effect of deleting the first node

   Deleting the first node means the head must point to the second node, which becomes the new first node.

3. Final Answer:

   It moves to the next node in the list -> Option A

4. Quick Check:

   Head points to next node after deletion [OK]

Hint: Head always points to first node; update it to next after deletion [OK]

Common Mistakes:

• Forgetting to update head pointer
• Setting head to null without checking list
• Pointing head to last node incorrectly

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

easy

A. head = head.next;

B. head.next = head;

C. head = null.next;

D. head.next = null;

Solution

1. Step 1: Understand the head pointer update

   To delete the first node, head must point to the second node, which is head.next.

2. Step 2: Check each option

   head = head.next; correctly assigns head to head.next. Others either cause errors or wrong assignments.

3. Final Answer:

   head = head.next; -> Option A

4. Quick Check:

   Assign head to next node to delete first [OK]

Hint: Assign head to head.next to delete first node [OK]

Common Mistakes:

• Using head.next = head which reverses links
• Trying to access null.next causing error
• Setting head.next to null which breaks list

3. Given the linked list: 10 -> 20 -> 30 -> null, what will be the list after deleting the node at the beginning using head = head.next;?

medium

A. 10 -> 20 -> 30 -> null

B. 20 -> 30 -> null

C. 30 -> null

D. null

Solution

1. Step 1: Identify the initial list

   The list starts as 10 -> 20 -> 30 -> null, with head pointing to 10.

2. Step 2: Apply deletion by moving head

   Setting head = head.next moves head to 20, so the list becomes 20 -> 30 -> null.

3. Final Answer:

   20 -> 30 -> null -> Option B

4. Quick Check:

   Head moves from 10 to 20 after deletion [OK]

Hint: After deletion, head points to second node, list starts there [OK]

Common Mistakes:

• Not updating head pointer
• Assuming first node remains
• Confusing node values after deletion

4. What is wrong with this code snippet for deleting the first node in a singly linked list?

if (head == null) {
    System.out.println("List is empty");
} else {
    head.next = head;
}

medium

A. It correctly deletes the first node

B. It throws a NullPointerException

C. It sets head to null, losing the list

D. It causes the head to point to itself, creating a cycle

Solution

1. Step 1: Analyze the assignment head.next = head

   This sets the next pointer of the first node to point back to itself, creating a cycle.

2. Step 2: Understand the impact on deletion

   The head pointer is not updated, so the first node is not removed and the list structure is broken.

3. Final Answer:

   It causes the head to point to itself, creating a cycle -> Option D

4. Quick Check:

   Incorrect pointer assignment creates cycle [OK]

Hint: Assign head = head.next to delete; avoid head.next = head [OK]

Common Mistakes:

• Confusing head.next = head with head = head.next
• Not checking for empty list before deletion
• Ignoring pointer updates causing cycles

5. You have a singly linked list with nodes: 5 -> 15 -> 25 -> 35 -> null. After deleting the first node twice using head = head.next;, what will be the final list?

hard

A. 35 -> null

B. 15 -> 25 -> 35 -> null

C. 25 -> 35 -> null

D. null

Solution

1. Step 1: Initial list and first deletion

   Start: 5 -> 15 -> 25 -> 35 -> null. After first deletion, head moves to 15, list is 15 -> 25 -> 35 -> null.

2. Step 2: Second deletion

   After second deletion, head moves to 25, list is 25 -> 35 -> null.

3. Final Answer:

   25 -> 35 -> null -> Option C

4. Quick Check:

   Two deletions remove first two nodes [OK]

Hint: Each deletion moves head to next node, removing first node [OK]

Common Mistakes:

• Deleting only once instead of twice
• Confusing node values after multiple deletions
• Not updating head pointer correctly each time