Delete Node at End in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the linked list is empty before deletion.

DSA Java

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

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

Atail

Bhead

Cnull

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if head equals tail instead of null.

Using 'next' instead of null.

We check if head is null to know if the list is empty before deleting.

2fill in blank

medium

Complete the code to handle the case when the list has only one node.

DSA Java

if (head.next == [1]) {
    return null;
}

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

Ahead

Bhead.next

Ctail

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if head.next equals head.

Using tail instead of null.

If head.next is null, it means only one node exists, so deleting it returns null.

3fill in blank

hard

Fix the error in the loop condition to find the second last node.

DSA Java

while (current.next.[1] != null) {
    current = current.next;
}

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

Anext.next

Bprev

Cnext.prev

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using current.next instead of current.next.next.

Using prev which is not defined in singly linked list.

We check current.next.next != null to stop at second last node before last node.

4fill in blank

hard

Fill both blanks to correctly remove the last node.

DSA Java

Node current = head;
while (current.next.[1] != null) {
    current = current.next;
}
current.next = [2];

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

Anext

Bprev

Cnull

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Setting current.next to head instead of null.

Using prev which is not defined.

We loop while current.next.next != null to reach second last node, then set current.next to null to delete last node.

5fill in blank

hard

Fill all three blanks to complete the delete last node method.

DSA Java

public Node deleteLast(Node head) {
    if (head == [1]) {
        return null;
    }
    if (head.next == [2]) {
        return null;
    }
    Node current = head;
    while (current.next.[3] != null) {
        current = current.next;
    }
    current.next = null;
    return head;
}

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

Anull

Bhead

Cnext

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of null for empty check.

Using tail which is undefined.

Loop condition using current.next instead of current.next.next.

Check if head is null or head.next is null to handle empty or single node list. Loop while current.next.next != null to find second last node.

Practice

1. What does the operation Delete Node at End do in a singly linked list?

easy

A. Removes the last node from the list

B. Removes the first node from the list

C. Adds a new node at the end of the list

D. Adds a new node at the beginning of the list

Solution

1. Step 1: Understand the operation meaning

   Deleting a node at the end means removing the last node in the linked list.

2. Step 2: Identify the correct description

   Removing the last node matches Removes the last node from the list, while others describe adding or removing nodes at different positions.

3. Final Answer:

   Removes the last node from the list -> Option A

4. Quick Check:

   Delete Node at End = Removes last node [OK]

Hint: Deleting at end always removes the last node [OK]

Common Mistakes:

• Confusing delete at end with delete at beginning
• Thinking it adds a node instead of removing
• Mixing up first and last node operations

2. Which of the following is the correct Java syntax to delete the last node in a singly linked list named list assuming you have a method deleteAtEnd()?

easy

A. list.deleteAtEnd();

B. deleteAtEnd.list();

C. list.deleteAtEnd;

D. list.deleteAtEnd[];

Solution

1. Step 1: Identify method call syntax in Java

   Calling a method on an object uses dot notation with parentheses: object.methodName();

2. Step 2: Match correct syntax

   list.deleteAtEnd(); uses correct syntax: list.deleteAtEnd(); others have syntax errors or wrong usage.

3. Final Answer:

   list.deleteAtEnd(); -> Option A

4. Quick Check:

   Method call syntax = object.method() [OK]

Hint: Method calls need parentheses after name [OK]

Common Mistakes:

• Omitting parentheses when calling methods
• Using brackets [] instead of parentheses ()
• Reversing object and method names

3. Consider the following Java code for a singly linked list:

class Node {
  int data;
  Node next;
  Node(int d) { data = d; next = null; }
}

class LinkedList {
  Node head;

  void deleteAtEnd() {
    if (head == null) return;
    if (head.next == null) {
      head = null;
      return;
    }
    Node temp = head;
    while (temp.next.next != null) {
      temp = temp.next;
    }
    temp.next = null;
  }

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

public class Main {
  public static void main(String[] args) {
    LinkedList list = new LinkedList();
    list.head = new Node(1);
    list.head.next = new Node(2);
    list.head.next.next = new Node(3);
    list.deleteAtEnd();
    list.printList();
  }
}

What is the output after running this code?

medium

A. 1 -> 2 -> 3 -> null

B. 1 -> 2 -> null

C. 2 -> 3 -> null

D. null

Solution

1. Step 1: Understand initial list and deleteAtEnd()

   The list starts as 1 -> 2 -> 3 -> null. The deleteAtEnd() removes the last node (3).

2. Step 2: Trace deleteAtEnd() method

   It traverses to node with data 2, sets its next to null, removing node 3.

3. Final Answer:

   1 -> 2 -> null -> Option B

4. Quick Check:

   Last node removed, list ends at 2 [OK]

Hint: Deleting end removes last node, list shortens by one [OK]

Common Mistakes:

• Forgetting to update the second last node's next to null
• Assuming head changes when list has multiple nodes
• Printing old list without deletion

4. The following Java method is intended to delete the last node of a singly linked list. What is the error?

void deleteAtEnd() {
  if (head == null) return;
  Node temp = head;
  while (temp.next != null) {
    temp = temp.next;
  }
  temp = null;
}

medium

A. It causes a NullPointerException

B. It does not handle empty list

C. It deletes the head node incorrectly

D. It does not update the second last node's next pointer

Solution

1. Step 1: Analyze the loop and pointer updates

   The loop moves temp to the last node (where temp.next is null). Setting temp = null only changes local pointer, not list links.

2. Step 2: Identify missing update to second last node

   The second last node's next pointer is not set to null, so the last node remains linked.

3. Final Answer:

   It does not update the second last node's next pointer -> Option D

4. Quick Check:

   Must update second last node's next to null [OK]

Hint: Set second last node's next to null, not just temp = null [OK]

Common Mistakes:

• Setting temp = null only changes local variable
• Not handling single-node list case
• Ignoring list head update if only one node

5. You have a singly linked list with nodes containing values: 10 -> 20 -> 30 -> 40 -> null. You want to delete the last node and then add a new node with value 50 at the end. Which sequence of operations correctly achieves this?

hard

A. Call addAtEnd(50) only

B. Call addAtEnd(50), then call deleteAtEnd()

C. Call deleteAtEnd(), then call addAtEnd(50)

D. Call deleteAtEnd() twice, then addAtEnd(50)

Solution

1. Step 1: Delete the last node

   Calling deleteAtEnd() removes node with value 40, list becomes 10 -> 20 -> 30 -> null.

2. Step 2: Add new node with value 50 at end

   Calling addAtEnd(50) appends node 50, list becomes 10 -> 20 -> 30 -> 50 -> null.

3. Final Answer:

   Call deleteAtEnd(), then call addAtEnd(50) -> Option C

4. Quick Check:

   Delete last, then add new node [OK]

Hint: Delete old last node before adding new one [OK]

Common Mistakes:

• Adding new node before deleting old last node
• Deleting twice unnecessarily
• Not deleting at all before adding