Delete Node at End in DSA Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Delete Node at End' mean in a linked list?

It means removing the last node from a linked list, so the second last node becomes the new end.

beginner

In a singly linked list, why do we need to traverse the list to delete the last node?

Because we only have a reference to the head and each node points forward, we must reach the second last node to update its next pointer to null.

beginner

What happens if you delete the last node in a linked list with only one node?

The list becomes empty, so the head pointer should be set to null.

intermediate

Show the Java code snippet to delete the last node in a singly linked list.

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

beginner

What is the time complexity of deleting the last node in a singly linked list?

O(n), because you need to traverse the list to find the second last node.

What pointer do you update when deleting the last node in a singly linked list?

A The next pointer of the second last node

B The head pointer

C The next pointer of the last node

D The previous pointer of the last node

You update the next pointer of the second last node to null to remove the last node.

If a linked list has only one node, what happens after deleting the last node?

A The head points to a new node

B The node points to itself

C The list becomes empty (head is null)

D The list remains unchanged

Deleting the only node makes the list empty, so head should be set to null.

What is the time complexity to delete the last node in a singly linked list?

A O(1)

B O(n^2)

C O(log n)

D O(n)

You must traverse the list to find the second last node, so it takes O(n) time.

Which node do you stop at to delete the last node in a singly linked list?

A The last node

B The second last node

C The middle node

D The head node

You stop at the second last node to update its next pointer to null.

What happens if you try to delete the last node from an empty linked list?

A Nothing, list remains empty

B Error occurs

C A new node is created

D The head becomes a new node

If the list is empty, deleting does nothing and the list stays empty.

Explain step-by-step how to delete the last node in a singly linked list.

Think about special cases and how to find the node before the last.

Write Java code to delete the last node of a singly linked list and explain each line.

Focus on traversal and pointer updates.

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