Delete Node at Beginning in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update the head pointer when deleting the first node in a linked list.

DSA Rust

self.head = [1];

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

Aself.head

Bself.head.clone()

CNone

Dself.head.as_mut().and_then(|node| node.next.take())

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning head to itself without change.

Assigning head to None without checking next.

Cloning head instead of moving next node.

To delete the first node, we update the head to point to the next node. Using self.head.as_mut().and_then(|node| node.next.take()) moves ownership of the next node to head.

2fill in blank

medium

Complete the code to check if the linked list is empty before deleting the first node.

DSA Rust

if self.head.is_[1]() {
    return None;
}

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

Aempty

Bsome

Cnone

Dnil

Attempts:

3 left

💡 Hint

Common Mistakes

Using is_empty() which is not a method on Option in this context.

Using is_some() which checks for presence, not absence.

Using incorrect method names like none() or nil().

We use is_none() to check if the head is None, meaning the list is empty.

3fill in blank

hard

Fix the error in the code to properly return the value of the deleted node.

DSA Rust

let old_head = self.head.take();
if let Some(node) = old_head {
    self.head = node.next;
    return Some(node.[1]);
} else {
    return None;
}

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

Adata

Bvalue

Cval

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect field names like val or item which do not exist.

Trying to return the whole node instead of its value.

The node's stored value is accessed by the field value in this linked list implementation.

4fill in blank

hard

Fill both blanks to safely update the head and return the deleted node's value.

DSA Rust

let old_head = self.head.[1]();
if let Some(node) = old_head {
    self.head = node.[2];
    Some(node.value)
} else {
    None
}

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

Atake

Bclone

Cnext

Dunwrap

Attempts:

3 left

💡 Hint

Common Mistakes

Using clone() which copies instead of moves ownership.

Using unwrap() which panics if None.

Assigning head to wrong field.

We use take() to move the head out safely, then assign node.next to head to delete the first node.

5fill in blank

hard

Fill all three blanks to implement the full delete at beginning function returning the deleted value.

DSA Rust

pub fn delete_at_beginning(&mut self) -> Option<T> {
    let old_head = self.head.[1]();
    if let Some(node) = old_head {
        self.head = node.[2];
        return Some(node.[3]);
    }
    None
}

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

Atake

Bnext

Cvalue

Dclone

Attempts:

3 left

💡 Hint

Common Mistakes

Using clone() instead of take().

Returning the whole node instead of its value.

Not updating head to the next node.

This function moves the head out with take(), updates head to the next node, and returns the deleted node's value.

Practice

1. What does deleting a node at the beginning of a singly linked list do to the list?

easy

A. Deletes all nodes in the list

B. Removes the last node and updates the tail

C. Removes the first node and updates the head to the next node

D. Removes a node from the middle of the list

Solution

1. Step 1: Understand the head pointer role

   The head points to the first node in the list, so deleting the first node means changing the head.

2. Step 2: Update the head to the next node

   After removing the first node, the head should point to the second node, effectively removing the first node from the list.

3. Final Answer:

   Removes the first node and updates the head to the next node -> Option C

4. Quick Check:

   Delete at beginning = remove first node [OK]

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

Common Mistakes:

• Trying to remove the last node instead of the first
• Not updating the head pointer after deletion
• Deleting all nodes instead of just one

2. Which Rust code snippet correctly deletes the first node of a singly linked list stored in a variable head?

easy

A. head = head.take().and_then(|node| node.next);

B. head = head.unwrap().next;

C. head = head.next;

D. head.next = head;

Solution

1. Step 1: Understand Rust Option handling for linked lists

   In Rust, linked lists often use Option. To delete the first node, we take the head and replace it with its next node safely.

2. Step 2: Use take() and and_then() to update head

   head.take() removes the current head, and and_then(|node| node.next) sets head to the next node, deleting the first.

3. Final Answer:

   head = head.take().and_then(|node| node.next); -> Option A

4. Quick Check:

   Use take() and and_then() to delete first node [OK]

Hint: Use take() and and_then() to update head safely [OK]

Common Mistakes:

• Trying to assign head.next directly without handling Option
• Using unwrap() which can panic if head is None
• Assigning head.next to head causing infinite loop

3. What will be the output linked list after deleting the first node from this Rust linked list?

let mut head = Some(Box::new(Node { value: 10, next: Some(Box::new(Node { value: 20, next: Some(Box::new(Node { value: 30, next: None })) })) }));
head = head.take().and_then(|node| node.next);

Print the list values in order.

medium

A. []

B. [10, 20, 30]

C. [30]

D. [20, 30]

Solution

1. Step 1: Initial list values

   The list starts as 10 -> 20 -> 30 -> None.

2. Step 2: Delete the first node

   Using head.take().and_then(|node| node.next) removes the node with value 10 and sets head to node with value 20.

3. Final Answer:

   [20, 30] -> Option D

4. Quick Check:

   After deletion, list starts at 20 [OK]

Hint: Deleting first node removes head value [OK]

Common Mistakes:

• Forgetting to update head, so list stays same
• Assuming deletion removes last node
• Confusing node values order after deletion

4. Identify the error in this Rust code that tries to delete the first node of a linked list:

fn delete_first(mut head: Option) -> Option {
    head = head.unwrap().next;
    head
}

medium

A. Using unwrap() without checking if head is None causes panic

B. The function does not return the updated head

C. head.next is assigned incorrectly

D. The function should take &mut head instead of ownership

Solution

1. Step 1: Check unwrap() usage

   Calling unwrap() on an Option that might be None will cause the program to panic at runtime.

2. Step 2: Safe deletion requires handling None

   Before unwrap(), code should check if head is Some or use methods like take() and and_then() to avoid panic.

3. Final Answer:

   Using unwrap() without checking if head is None causes panic -> Option A

4. Quick Check:

   unwrap() on None causes panic [OK]

Hint: Never unwrap() without checking Option first [OK]

Common Mistakes:

• Ignoring possibility of empty list (None)
• Not returning updated head properly
• Confusing ownership and borrowing in function

5. Given a Rust singly linked list where each node contains an integer, write the correct way to delete the first node and return the updated list head. Which code snippet correctly handles the edge case when the list is empty?

hard

A. fn delete_first(head: Option) -> Option {
head.unwrap().next
}

B. fn delete_first(mut head: Option) -> Option {
head = head.take().and_then(|node| node.next);
head
}

C. fn delete_first(head: Option) -> Option {
if head.is_some() {
head.unwrap()
} else {
None
}
}

D. fn delete_first(head: Option) -> Option {
head.next
}

Solution

1. Step 1: Handle Option safely with take() and and_then()

   Using head.take().and_then(|node| node.next) safely removes the first node and returns the next node or None if empty.

2. Step 2: Return updated head

   Assign the result back to head and return it, ensuring the function works for empty and non-empty lists.

3. Final Answer:

   fn delete_first(mut head: Option) -> Option { head = head.take().and_then(|node| node.next); head } -> Option B

4. Quick Check:

   Use take() and and_then() for safe deletion [OK]

Hint: Use take() and and_then() to handle empty list safely [OK]

Common Mistakes:

• Using unwrap() without checking for None
• Accessing head.next directly on Option type
• Not returning the updated head after deletion