Delete Node at End in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Rust

if self.head.is_[1]() {
    return;
}

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

Aempty

Bnone

Cnull

Dsome

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'empty' or 'null' which are not Rust Option methods.

Confusing is_some() with is_none().

In Rust, Option types use is_none() to check if the value is empty (None).

2fill in blank

medium

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

DSA Rust

if self.head.as_ref().unwrap().next.is_[1]() {
    self.head = None;
    return;
}

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

Asome

Bnull

Cempty

Dnone

Attempts:

3 left

💡 Hint

Common Mistakes

Using is_some() which checks presence, not absence.

Using invalid method names like 'empty' or 'null'.

We check if the next pointer is None to know if there is only one node.

3fill in blank

hard

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

DSA Rust

while current.next.as_ref().unwrap().next.is_[1]() {
    current = current.next.as_mut().unwrap();
}

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

Asome

Bnone

Cempty

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using is_none() which stops too early.

Using invalid method names.

The loop continues while the next node's next exists (is_some()).

4fill in blank

hard

Fill both blanks to correctly remove the last node.

DSA Rust

let last_node = current.next.take();
current.next = [1];
// last_node is dropped here

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

ANone

BSome(Box::new(Node { val: 0, next: None }))

Ccurrent.next

DSome(current.next.unwrap())

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning Some values which keep nodes linked.

Assigning current.next to itself causing no change.

Setting current.next to None removes the last node.

5fill in blank

hard

Fill all three blanks to complete the delete at end function.

DSA Rust

pub fn delete_at_end(&mut self) {
    if self.head.is_[1]() {
        return;
    }
    if self.head.as_ref().unwrap().next.is_[2]() {
        self.head = [3];
        return;
    }
    let mut current = self.head.as_mut().unwrap();
    while current.next.as_ref().unwrap().next.is_some() {
        current = current.next.as_mut().unwrap();
    }
    current.next = None;
}

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

Anone

Bsome

CNone

DSome(Box::new(Node { val: 0, next: None }))

Attempts:

3 left

💡 Hint

Common Mistakes

Using is_some() instead of is_none() in checks.

Assigning Some instead of None to head.

The function checks if the list is empty (is_none()), then if only one node (next.is_none()), then sets head to None to delete it.

Practice

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

easy

A. Adds a new node at the end of the linked list

B. Removes the last node from the linked list

C. Removes the first node from the linked list

D. Searches for a node at the end of the linked list

Solution

1. Step 1: Understand the linked list structure

   A linked list is a chain of nodes where each node points to the next one.

2. Step 2: Identify the effect of deleting the last node

   Deleting the last node means removing the node that has no next node, effectively shortening the list by one node at the end.

3. Final Answer:

   Removes the last node from the linked list -> Option B

4. Quick Check:

   Delete Node at End = Remove last node [OK]

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

Common Mistakes:

• Confusing delete at end with delete at start
• Thinking it adds a node instead of removing
• Assuming it searches without deleting

2. Which of the following Rust code snippets correctly deletes the last node of a singly linked list?

easy

A. fn delete_end(head: &mut Option) { if head.is_none() { return; } let mut current = head.as_mut().unwrap(); while current.next.as_ref().unwrap().next.is_some() { current = current.next.as_mut().unwrap(); } current.next = None; }

B. fn delete_end(head: &mut Option) { *head = None; }

C. fn delete_end(head: &mut Option) { let mut current = head.as_mut().unwrap(); current.next = None; }

D. fn delete_end(head: &mut Option) { while head.is_some() { head = head.unwrap().next; } }

Solution

1. Step 1: Analyze the code logic for deleting last node

   fn delete_end(head: &mut Option) { if head.is_none() { return; } let mut current = head.as_mut().unwrap(); while current.next.as_ref().unwrap().next.is_some() { current = current.next.as_mut().unwrap(); } current.next = None; } traverses the list until the second last node and sets its next to None, removing the last node.

2. Step 2: Check other options for correctness

   fn delete_end(head: &mut Option) { *head = None; } deletes the entire list, not just last node. fn delete_end(head: &mut Option) { let mut current = head.as_mut().unwrap(); current.next = None; } incorrectly sets next of head only. fn delete_end(head: &mut Option) { while head.is_some() { head = head.unwrap().next; } } tries to reassign head incorrectly causing error.

3. Final Answer:

   Option A code correctly deletes the last node -> Option A

4. Quick Check:

   Traverse to second last node and set next to None [OK]

Hint: Traverse to second last node, then set next to None [OK]

Common Mistakes:

• Setting head to None deletes whole list
• Not checking for empty or single node list
• Incorrectly reassigning head pointer

3. Given the Rust linked list code below, what will be the printed output after deleting the last node?

struct Node { val: i32, next: Option }
fn print_list(head: &Option) {
  let mut current = head;
  while let Some(node) = current {
    print!("{} -> ", node.val);
    current = &node.next;
  }
  println!("null");
}
fn main() {
  let mut head = Some(Box::new(Node { val: 1, next: Some(Box::new(Node { val: 2, next: Some(Box::new(Node { val: 3, next: None })) })) }));
  delete_end(&mut head);
  print_list(&head);
}
fn delete_end(head: &mut Option) {
  if head.is_none() { return; }
  if head.as_ref().unwrap().next.is_none() { *head = None; return; }
  let mut current = head.as_mut().unwrap();
  while current.next.as_ref().unwrap().next.is_some() {
    current = current.next.as_mut().unwrap();
  }
  current.next = None;
}

medium

A. null

B. 1 -> 2 -> 3 -> null

C. 1 -> 2 -> null

D. 1 -> null

Solution

1. Step 1: Understand initial list and delete_end effect

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

2. Step 2: Trace print_list after deletion

   After deletion, list is 1 -> 2 -> null, so print_list outputs "1 -> 2 -> null".

3. Final Answer:

   1 -> 2 -> null -> Option C

4. Quick Check:

   Last node removed, list ends at 2 [OK]

Hint: Deleting last node removes final value from print output [OK]

Common Mistakes:

• Expecting original list unchanged
• Confusing print output format
• Not handling single node list case

4. The following Rust function to delete the last node of a linked list causes a runtime panic. What is the error?

fn delete_end(head: &mut Option) {
  let mut current = head.as_mut().unwrap();
  while current.next.is_some() {
    current = current.next.as_mut().unwrap();
  }
  current.next = None;
}

medium

A. It panics because it sets current to None instead of current.next

B. It panics because it modifies head directly without checking

C. It panics because it never stops the loop

D. It panics because it tries to unwrap None when list is empty

Solution

1. Step 1: Locate the unwrap without check

   let mut current = head.as_mut().unwrap(); executes without prior if head.is_none() { return; }, causing panic on empty list when as_mut() returns None and unwrap panics.

2. Step 2: Verify other options

   The code does not modify head directly. The while loop terminates when current.next.is_none(). Setting current.next = None after reaching the last node causes no panic.

3. Final Answer:

   It panics because it tries to unwrap None when list is empty -> Option D

4. Quick Check:

   head.as_mut().unwrap() without empty check [OK]

Hint: Check head.is_none() before any unwrap on head [OK]

Common Mistakes:

• No check for empty list before unwrap
• Not checking for empty or single node list
• Looping until current.next is None instead of second last

5. You have a singly linked list with nodes containing values [10, 20, 30, 40]. Write a Rust function to delete the last node and return the updated list head. Which of the following implementations correctly handles the edge case when the list has only one node?

hard

A. fn delete_end(head: &mut Option) { if head.is_none() { return; } if head.as_ref().unwrap().next.is_none() { *head = None; return; } let mut current = head.as_mut().unwrap(); while current.next.as_ref().unwrap().next.is_some() { current = current.next.as_mut().unwrap(); } current.next = None; }

B. fn delete_end(head: &mut Option) { let mut current = head.as_mut().unwrap(); while current.next.is_some() { current = current.next.as_mut().unwrap(); } current = None; }

C. fn delete_end(head: &mut Option) { if head.is_none() { return; } let mut current = head.as_mut().unwrap(); while current.next.is_some() { current = current.next.as_mut().unwrap(); } current.next = None; }

D. fn delete_end(head: &mut Option) { *head = None; }

Solution

1. Step 1: Check for empty and single node list

   fn delete_end(head: &mut Option) { if head.is_none() { return; } if head.as_ref().unwrap().next.is_none() { *head = None; return; } let mut current = head.as_mut().unwrap(); while current.next.as_ref().unwrap().next.is_some() { current = current.next.as_mut().unwrap(); } current.next = None; } correctly checks if list is empty or has only one node, setting head to None in that case.

2. Step 2: Traverse to second last node and delete last

   fn delete_end(head: &mut Option) { if head.is_none() { return; } if head.as_ref().unwrap().next.is_none() { *head = None; return; } let mut current = head.as_mut().unwrap(); while current.next.as_ref().unwrap().next.is_some() { current = current.next.as_mut().unwrap(); } current.next = None; } then traverses to second last node and sets its next to None, deleting last node properly.

3. Final Answer:

   Option A correctly handles all cases including single node list -> Option A

4. Quick Check:

   Check empty/single node, then delete last node [OK]

Hint: Always check if list has one node before deleting last [OK]

Common Mistakes:

• Not handling single node list causing panic
• Setting current = None instead of current.next = None
• Deleting entire list instead of last node