Traversal of Circular Linked List in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Circular Linked List Traversal

What is the printed output of the following code that traverses a circular linked list starting from the head node?

DSA Python

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

# Create nodes
head = Node(10)
second = Node(20)
third = Node(30)

# Link nodes in circular fashion
head.next = second
second.next = third
third.next = head

# Traverse circular linked list
current = head
output = []
while True:
    output.append(str(current.data))
    current = current.next
    if current == head:
        break
print(' -> '.join(output) + ' -> null')

A 10 -> 20 -> null

B 10 -> 20 -> 30 -> 10 -> null

C RuntimeError: infinite loop

D 10 -> 20 -> 30 -> null

💡 Hint

Remember that traversal stops when we reach the head node again.

The traversal starts at head (10), moves to 20, then 30, and stops before repeating head again. So output is '10 -> 20 -> 30 -> null'.

🧠 Conceptual

intermediate

Number of Nodes in Circular Linked List

Given a circular linked list where the head node points back to itself after the last node, how many nodes will be counted by traversing until you reach the head again?

A The number of nodes in the list

B One less than the number of nodes

C Infinite nodes because of the loop

D Zero nodes because head is repeated

💡 Hint

Traversal stops when you reach the head again, so count all unique nodes once.

Traversal counts each node once until it reaches the head again, so the count equals the total number of nodes.

🔧 Debug

advanced

Identify the Bug in Circular Linked List Traversal

What error will occur when running this traversal code on a circular linked list?

DSA Python

current = head
while current.next != head:
    print(current.data, end=' -> ')
    current = current.next
print(current.data, end=' -> null')

A No error, prints all nodes correctly

B Skips the last node in the list

C Infinite loop occurs

D AttributeError because current is None

💡 Hint

Check if the last node's data is printed or skipped.

The while loop runs while current.next != head, printing data for all nodes except the last inside the loop, then prints the last node's data (' -> null') after the loop. All nodes are printed correctly with no error.

📝 Syntax

advanced

Identify Syntax Error in Circular Linked List Traversal

Which option contains a syntax error when trying to traverse a circular linked list?

DSA Python

current = head
while True
    print(current.data)
    current = current.next
    if current == head:
        break

A No syntax error

B Missing colon after while True

C Incorrect comparison operator in if statement

D Missing parentheses in print statement

💡 Hint

Check the syntax of the while loop line.

The while loop line is missing a colon at the end, causing a syntax error.

🚀 Application

expert

Result of Modifying Circular Linked List During Traversal

Consider this code that removes the node with data 20 during traversal of a circular linked list. What is the printed output after modification?

DSA Python

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

head = Node(10)
second = Node(20)
third = Node(30)
head.next = second
second.next = third
third.next = head

current = head
prev = None
output = []
while True:
    if current.data == 20:
        prev.next = current.next
        current = current.next
        continue
    output.append(str(current.data))
    prev = current
    current = current.next
    if current == head:
        break
print(' -> '.join(output) + ' -> null')

A RuntimeError due to NoneType attribute access

B 10 -> 20 -> 30 -> null

C 10 -> 30 -> null

D Infinite loop without stopping

💡 Hint

Trace the values of prev and current step by step, especially during deletion and the continue statement.

When current reaches 20, prev is 10, so prev.next = 30 removes 20 safely. The continue skips appending 20. Then appends 10 (earlier) and 30, stopping before head again. Output: 10 -> 30 -> null.