Why Circular Linked List and Real World Use Cases in DSA Rust - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a circular linked list node that points to itself.

DSA Rust

let node = Node { value: 10, next: [1] };

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ANone

BSome(Box::new(Node { value: 10, next: None }))

CSome(Box::new(node))

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to None breaks the circular link.

Creating a new node instead of pointing to the existing node.

In a circular linked list, the node's next pointer points back to itself, creating a loop. Using Some(Box::new(node)) achieves this self-reference.

2fill in blank

medium

Complete the code to traverse a circular linked list once starting from head.

DSA Rust

let mut current = &head;
loop {
    println!("{}", current.value);
    current = current.next.as_ref().unwrap();
    if current as *const _ == [1] as *const _ {
        break;
    }
}

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A&head.next

B&head

C&current

D&head.value

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing to head.next instead of head.

Comparing values instead of node pointers.

To stop after one full circle, compare the current node's pointer to the head's pointer. When they match, the loop ends.

3fill in blank

hard

Fix the error in the code that inserts a new node after the head in a circular linked list.

DSA Rust

let new_node = Box::new(Node { value: 20, next: head.next.take() });
head.next = Some([1]);

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Anew_node

Bnew_node.next

Chead

Dhead.next

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning head.next to new_node.next instead of new_node.

Assigning head.next to head or head.next.

We assign the new node itself to head.next to insert it after head. Using new_node.next would be incorrect.

4fill in blank

hard

Fill both blanks to complete the function that checks if a circular linked list contains a value.

DSA Rust

fn contains(head: &Node, target: i32) -> bool {
    let mut current = head;
    loop {
        if current.value == [1] {
            return true;
        }
        current = current.next.as_ref().unwrap();
        if current as *const _ == [2] as *const _ {
            break;
        }
    }
    false
}

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Atarget

Bhead

Ccurrent

Dtarget.value

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing to target.value instead of target.

Stopping loop when current equals target instead of head.

The function compares each node's value to the target. It stops when it loops back to the head node.

5fill in blank

hard

Fill all three blanks to create a circular linked list from a vector of values.

DSA Rust

fn create_circular_list(values: Vec<i32>) -> Option<Box<Node>> {
    if values.is_empty() {
        return None;
    }
    let mut head = Box::new(Node { value: values[0], next: None });
    let mut current = &mut head;
    for &val in &values[1..] {
        current.next = Some(Box::new(Node { value: val, next: None }));
        current = current.next.as_mut().unwrap();
    }
    current.next = Some([1]);
    Some(head)
}

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Ahead

BBox::new(head)

C*head

Dhead.next

Attempts:

3 left

💡 Hint

Common Mistakes

Pointing last node's next to head.next instead of head.

Trying to box head again causing ownership errors.

To make the list circular, the last node's next points back to the head node.

Practice

1. What is the main advantage of using a circular linked list over a regular singly linked list?

easy

A. It automatically sorts the elements.

B. It uses less memory than a singly linked list.

C. It allows continuous traversal without reaching a null end.

D. It prevents duplicate elements.

Solution

1. Step 1: Understand traversal in singly linked list

   A singly linked list ends with a null pointer, so traversal stops at the last node.

2. Step 2: Understand traversal in circular linked list

   A circular linked list connects the last node back to the first, allowing infinite traversal without null.

3. Final Answer:

   It allows continuous traversal without reaching a null end. -> Option C

4. Quick Check:

   Continuous traversal = Advantage of circular linked list [OK]

Hint: Circular lists loop back to start, no null end [OK]

Common Mistakes:

• Thinking circular lists save memory
• Assuming circular lists sort data automatically
• Believing circular lists prevent duplicates

2. Which of the following is the correct way to link the last node to the first node in a circular linked list in Rust?

easy

A. last_node.next = Some(first_node);

B. last_node.next = Some(Box::new(first_node));

C. last_node.next = None;

D. last_node.next = Some(&first_node);

Solution

1. Step 1: Understand Rust pointer types for linked lists

   In Rust, linked lists use Option or references to link nodes.

2. Step 2: Linking last node to first node

   To make it circular, last node's next should point to the first node wrapped in Some without extra boxing.

3. Final Answer:

   last_node.next = Some(first_node); -> Option A

4. Quick Check:

   Link last to first with Some(node) [OK]

Hint: Use Some(node) to link nodes, not None or Box::new [OK]

Common Mistakes:

• Assigning None breaks circularity
• Using Box::new duplicates node unnecessarily
• Using references without lifetimes causes errors

3. Consider this Rust code snippet for a circular linked list traversal:

let mut current = Some(&head);
for _ in 0..5 {
    if let Some(node) = current {
        print!("{} ", node.value);
        current = node.next.as_deref();
    }
}

If the list has values 10 -> 20 -> 30 -> (back to 10), what will be the printed output?

medium

A. 10 20 30 10 20

B. 10 20 30 30 30

C. 10 20 30 20 10

D. 10 20 30 10 30

Solution

1. Step 1: Understand list structure and traversal

   The list is circular: 10 -> 20 -> 30 -> back to 10. Traversal loops through these nodes repeatedly.

2. Step 2: Trace the loop for 5 iterations

   Iteration 1: print 10, move to 20
   Iteration 2: print 20, move to 30
   Iteration 3: print 30, move to 10
   Iteration 4: print 10, move to 20
   Iteration 5: print 20, move to 30

3. Final Answer:

   10 20 30 10 20 -> Option A

4. Quick Check:

   Loop repeats nodes in order [OK]

Hint: Circular list repeats nodes in order during traversal [OK]

Common Mistakes:

• Stopping traversal early at null
• Printing wrong node values after loop
• Confusing node references in Rust

4. Given this Rust code snippet for a circular linked list insertion:

fn insert_after(node: &mut Node, value: i32) {
    let new_node = Node { value, next: node.next.take() };
    node.next = Some(Box::new(new_node));
}

What is the bug in this code?

medium

A. It uses take() incorrectly causing data loss.

B. It causes infinite loop by linking node to itself.

C. It creates a new node without setting its value.

D. It does not update the last node's next to maintain circularity.

Solution

1. Step 1: Analyze insertion logic

   The function inserts a new node after the given node by adjusting pointers.

2. Step 2: Check circularity maintenance

   In a circular list, the last node's next must point to the head. This code does not update last node's next if insertion affects it.

3. Final Answer:

   It does not update the last node's next to maintain circularity. -> Option D

4. Quick Check:

   Maintain circular links after insertion [OK]

Hint: Always update last node's next to keep circular link [OK]

Common Mistakes:

• Ignoring circular link after insertion
• Misusing take() causing pointer loss
• Assuming new node auto-links circularly

5. Which real-world scenario best fits the use of a circular linked list?

hard

A. Caching web pages with least recently used eviction.

B. Implementing a music playlist that repeats songs endlessly.

C. Maintaining a sorted list of student grades.

D. Storing user login history in chronological order.

Solution

1. Step 1: Understand circular linked list use cases

   Circular linked lists are ideal when data needs to be accessed repeatedly in a loop without stopping.

2. Step 2: Match scenario to circular list

   A music playlist that repeats songs endlessly fits perfectly because after the last song, it loops back to the first.

3. Final Answer:

   Implementing a music playlist that repeats songs endlessly. -> Option B

4. Quick Check:

   Endless looping = circular list use case [OK]

Hint: Use circular lists for endless repeating sequences [OK]

Common Mistakes:

• Choosing sorted or chronological data for circular list
• Confusing caching with circular traversal
• Ignoring looping nature of circular lists