Circular vs Linear Linked List Key Difference in DSA Python - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a linked list is circular by comparing the next node of the last node.

DSA Python

def is_circular(head):
    if head is None:
        return False
    current = head
    while current.next is not None:
        current = current.next
    return current.next == [1]

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

Ahead

BNone

Ccurrent

Dhead.next

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if current.next is None instead of head

Confusing current with head.next

The last node's next points back to the head in a circular linked list, so we check if current.next == head.

2fill in blank

medium

Complete the code to traverse a circular linked list and print all node values once.

DSA Python

def print_circular_list(head):
    if head is None:
        return
    current = head
    while True:
        print(current.data)
        current = current.next
        if current == [1]:
            break

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

Ahead.next

BNone

Chead

Dcurrent.next

Attempts:

3 left

💡 Hint

Common Mistakes

Stopping when current.next is None

Using head.next instead of head

In a circular linked list, traversal stops when we reach the head again after one full cycle.

3fill in blank

hard

Fix the error in the code that tries to detect if a linked list is linear by checking if any node's next is None.

DSA Python

def is_linear(head):
    current = head
    while current is not None:
        if current.next == [1]:
            return True
        current = current.next
    return False

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

Acurrent.next

Bcurrent

Chead

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if current.next == head

Using current instead of None

In a linear linked list, the last node's next is None. So we check if current.next == None.

4fill in blank

hard

Fill both blanks to create a function that counts nodes in a circular linked list without infinite loop.

DSA Python

def count_nodes_circular(head):
    if head is None:
        return 0
    count = 1
    current = head.next
    while current != [1]:
        count += 1
        current = current.[2]
    return count

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

Ahead

Bnext

CNone

Dhead.next

Attempts:

3 left

💡 Hint

Common Mistakes

Using None instead of head to stop

Using head.next instead of next for traversal

We stop counting when current reaches head again. We move to the next node each iteration.

5fill in blank

hard

Fill all three blanks to create a function that converts a linear linked list to circular by linking last node to head.

DSA Python

def make_circular(head):
    if head is None:
        return None
    current = head
    while current.[1] is not [2]:
        current = current.[3]
    current.next = head
    return head

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

Anext

BNone

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of None in condition

Using head instead of next for traversal

We traverse until current.next is None (last node), then link current.next to head to make it circular.

Practice

1. What is the main difference between a circular linked list and a linear linked list?

easy

A. In a circular linked list, the last node points back to the first node, forming a circle.

B. In a linear linked list, the last node points back to the first node, forming a circle.

C. A circular linked list has no nodes.

D. A linear linked list always has only one node.

Solution

1. Step 1: Understand the structure of a linear linked list

   A linear linked list has nodes connected one after another, and the last node points to null, meaning the list ends.

2. Step 2: Understand the structure of a circular linked list

   In a circular linked list, the last node points back to the first node, creating a loop or circle.

3. Final Answer:

   In a circular linked list, the last node points back to the first node, forming a circle. -> Option A

4. Quick Check:

   Circular list loops back = A [OK]

Hint: Remember: circular means last node links to first [OK]

Common Mistakes:

• Thinking linear lists loop back to the start
• Confusing circular list with empty list
• Assuming linear list has only one node

2. Which of the following is the correct way to check if a linked list is circular in Python?

easy

A. if head.next == head: print('Circular')

B. if head.next == None: print('Circular')

C. if head == None: print('Circular')

D. if head.next == head.next.next: print('Circular')

Solution

1. Step 1: Understand the circular condition

   In a circular linked list with one node, the node's next points to itself (head.next == head).

2. Step 2: Check the given conditions

   if head.next == head: print('Circular') correctly checks if the next node is the head itself, indicating circularity.

3. Final Answer:

   if head.next == head: print('Circular') -> Option A

4. Quick Check:

   Node points to self means circular = A [OK]

Hint: Check if next points to head for circular list [OK]

Common Mistakes:

• Checking if next is None for circular list
• Confusing None with circular condition
• Using wrong pointer comparisons

3. What will be the output of the following code snippet?

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

head = Node(1)
second = Node(2)
third = Node(3)

head.next = second
second.next = third
third.next = head  # Circular link

current = head
count = 0
while count < 5:
    print(current.data, end=' ')
    current = current.next
    count += 1

medium

A. 1 2 3 3 3

B. 1 2 3 1 2

C. 1 2 3 4 5

D. 1 2 3 None None

Solution

1. Step 1: Understand the linked list structure

   The list has nodes 1 -> 2 -> 3, and the last node points back to head (1), making it circular.

2. Step 2: Trace the loop printing 5 nodes

   Starting at head (1), printing 1, then 2, then 3, then back to 1, then 2 again.

3. Final Answer:

   1 2 3 1 2 -> Option B

4. Quick Check:

   Circular list repeats nodes = D [OK]

Hint: Circular list repeats nodes in loop, watch count limit [OK]

Common Mistakes:

• Assuming None appears in circular list
• Expecting new nodes beyond 3
• Confusing circular with linear output

4. Find the error in this code that tries to create a circular linked list:

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

head = Node(10)
second = Node(20)
head.next = second
second.next = None  # Intended to be circular

medium

A. Node class is missing a circular flag.

B. head.next should be None to make it circular.

C. The data values should be equal for circular list.

D. second.next should point to head to make it circular.

Solution

1. Step 1: Understand circular linked list pointer

   For circular list, last node's next must point back to head or some previous node.

2. Step 2: Check the code's pointer assignment

   second.next is set to None, so list ends there, not circular.

3. Final Answer:

   second.next should point to head to make it circular. -> Option D

4. Quick Check:

   Last node points to head for circular = C [OK]

Hint: Last node must link back to head for circular list [OK]

Common Mistakes:

• Setting last node next to None in circular list
• Thinking data values affect circularity
• Missing pointer update for circular link

5. You want to traverse a circular linked list with unknown length without getting stuck in an infinite loop. Which approach is correct?

hard

A. Traverse nodes until you reach a node whose next is None.

B. Traverse nodes for a fixed number of steps equal to the number of nodes plus one.

C. Traverse nodes until you reach the head node again after the first visit.

D. Traverse nodes until you find a node with data equal to zero.

Solution

1. Step 1: Understand traversal in circular linked list

   Since circular lists have no None at the end, stopping at None won't work.

2. Step 2: Identify safe stopping condition

   Stop when you reach the head node again after the first visit to avoid infinite loop.

3. Final Answer:

   Traverse nodes until you reach the head node again after the first visit. -> Option C

4. Quick Check:

   Stop at head revisit to avoid infinite loop = B [OK]

Hint: Stop when you reach head again to avoid infinite loop [OK]

Common Mistakes:

• Stopping at None in circular list
• Using fixed steps without knowing length
• Stopping based on data value