Delete a Node from Circular Linked List in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Rust

if head [1] { return; }

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

A!= Some

B== Some

C== None

D!= None

Attempts:

3 left

💡 Hint

Common Mistakes

Using != None instead of == None

Checking for Some instead of None

We check if head is None to know if the list is empty.

2fill in blank

medium

Complete the code to find the node before the one to delete.

DSA Rust

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

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

Ahead.data

Bkey

Ccurrent.data

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with head.data instead of key

Using None which is invalid here

We look for the node whose next node has the data equal to the key to delete.

3fill in blank

hard

Fix the error in updating the head when deleting the head node.

DSA Rust

if current.next.as_ref().unwrap().data == head.as_ref().unwrap().data { head = [1]; }

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

Ahead.clone()

Bcurrent.next.clone()

CNone

Dcurrent.next.as_ref().unwrap().next.clone()

Attempts:

3 left

💡 Hint

Common Mistakes

Setting head to None

Setting head to current.next.clone() which is the deleted node

When deleting the head, update head to the next node after the current's next node.

4fill in blank

hard

Fill both blanks to correctly remove the node from the list.

DSA Rust

current.next = [1];
current.next.as_mut().unwrap().next = [2];

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

Acurrent.next.as_ref().unwrap().next.clone()

BNone

Chead.clone()

Dcurrent.next.clone()

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to None breaks the circle

Not updating the next pointer to head

Set current's next to skip the deleted node, and update the next pointer to head to maintain circularity.

5fill in blank

hard

Fill all three blanks to complete the function that deletes a node by key.

DSA Rust

fn delete_node(head: &mut Option<Box<Node>>, key: i32) {
    if head [1] { return; }
    let mut current = head.as_mut().unwrap();
    while current.next.as_ref().unwrap().data != [2] {
        current = current.next.as_mut().unwrap();
    }
    if current.next.as_ref().unwrap().data == head.as_ref().unwrap().data {
        head = [3];
    }
    current.next = current.next.as_ref().unwrap().next.clone();
}

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

A== None

Bkey

Ccurrent.next.as_ref().unwrap().next.clone()

Dhead.clone()

Attempts:

3 left

💡 Hint

Common Mistakes

Not checking for None

Using wrong variable for key

Incorrect head update

Check if head is None, find the node before the key, and update head to the next node after the deleted one.

Practice

1. What happens when you delete the only node in a circular linked list?

easy

A. The list points to itself indefinitely.

B. The list still contains the deleted node.

C. The list becomes empty (null).

D. The list throws an error.

Solution

1. Step 1: Understand the structure of a single-node circular linked list

   In a circular linked list with one node, the node's next pointer points to itself.

2. Step 2: Delete the only node

   Removing this node means no nodes remain, so the list becomes empty (null).

3. Final Answer:

   The list becomes empty (null). -> Option C

4. Quick Check:

   Single node deleted = empty list [OK]

Hint: Deleting the only node empties the list [OK]

Common Mistakes:

• Assuming the list still contains the deleted node
• Thinking the list points to itself after deletion
• Expecting an error instead of empty list

2. Which Rust syntax correctly declares a mutable circular linked list node struct with a next pointer?

easy

A. struct Node { data: i32, next: Option }

B. struct Node { data: i32, next: &Node }

C. struct Node { data: i32, next: Node }

D. struct Node { data: i32, next: Option> }

Solution

1. Step 1: Understand Rust ownership for circular references

   Rust disallows direct cyclic ownership. Using Rc allows multiple owners and interior mutability.

2. Step 2: Identify correct syntax for mutable circular linked list node

   struct Node { data: i32, next: Option> } uses Option> which supports cycles and mutability safely.

3. Final Answer:

   struct Node { data: i32, next: Option> } -> Option D

4. Quick Check:

   Use Rc for circular mutable nodes [OK]

Hint: Use Rc and RefCell for mutable circular references in Rust [OK]

Common Mistakes:

• Using plain Box<Node> causes ownership errors
• Using references (&Node) disallows ownership
• Using Node directly causes infinite size error

3. Given this Rust code snippet deleting a node with value 3 from a circular linked list:

let mut head = create_circular_list(vec![1, 2, 3, 4]); delete_node(&mut head, 3); print_list(&head);

What is the printed output?

medium

A. 1 -> 2 -> 4 -> 1 (circular)

B. 1 -> 2 -> 3 -> 4 -> 1 (circular)

C. 2 -> 3 -> 4 -> 2 (circular)

D. 1 -> 2 -> 4 -> null

Solution

1. Step 1: Understand the initial list

   The list is circular with nodes 1, 2, 3, 4 linked in a loop.

2. Step 2: Delete node with value 3

   Node 3 is removed, so the list becomes 1 -> 2 -> 4, then back to 1.

3. Final Answer:

   1 -> 2 -> 4 -> 1 (circular) -> Option A

4. Quick Check:

   Deleted 3, list loops 1-2-4 [OK]

Hint: Deleting node removes it, links neighbors circularly [OK]

Common Mistakes:

• Forgetting to link node 2 to node 4
• Printing null instead of circular loop
• Not deleting the correct node

4. Identify the bug in this Rust function snippet for deleting a node from a circular linked list:

fn delete_node(head: &mut Option>, key: i32) { let mut curr = head.clone().unwrap(); while curr.borrow().data != key { curr = curr.borrow().next.clone().unwrap(); } let next_node = curr.borrow().next.clone(); curr.borrow_mut().next = next_node.unwrap().borrow().next.clone(); }

medium

A. It causes infinite loop if key not found.

B. It does not handle deleting the head node correctly.

C. It leaks memory by not freeing nodes.

D. It uses unwrap() unsafely causing panic.

Solution

1. Step 1: Analyze the while loop condition

   The loop continues until curr's data equals key, but no check if key exists, so it loops infinitely if key missing.

2. Step 2: Check for missing exit condition

   Without a break or stop when full circle is done, infinite loop occurs if key not found.

3. Final Answer:

   It causes infinite loop if key not found. -> Option A

4. Quick Check:

   No key check = infinite loop risk [OK]

Hint: Always check for key existence to avoid infinite loops [OK]

Common Mistakes:

• Assuming key always exists
• Not checking for full circle traversal
• Ignoring unwrap() panic risks

5. How would you delete the head node from a circular linked list in Rust while maintaining the circular structure?

hard

A. Replace head data with next node data and delete next node.

B. Find the last node, set its next to head's next, then update head to head's next.

C. Delete head and leave the last node pointing to old head.

D. Set head to None directly without updating other nodes.

Solution

1. Step 1: Locate the last node in the circular list

   The last node points back to head; find it by traversing until next points to head.

2. Step 2: Update last node's next pointer and head

   Set last node's next to head's next node, then update head to head's next to maintain circularity.

3. Final Answer:

   Find last node, link it to head's next, update head to head's next. -> Option B

4. Quick Check:

   Update last node and head to delete head safely [OK]

Hint: Link last node to new head, then update head [OK]

Common Mistakes:

• Setting head to None breaks circularity
• Not updating last node's next pointer
• Deleting head without adjusting links