Traversal and Printing a Linked List in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Traversing a Linked List

What is the printed output of the linked list after running this traversal code?

DSA Python

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

head = Node(1)
head.next = Node(2)
head.next.next = Node(3)

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

A 1 -> 2 -> 3 -> null

B null

C 3 -> 2 -> 1 -> null

D 1 -> 2 -> null

💡 Hint

Think about how the traversal moves from the head node to the end.

The code starts at the head node and prints each node's data followed by '->'. It stops when current is None, then prints 'null'. So the output is '1 -> 2 -> 3 -> null'.

❓ Predict Output

intermediate

What happens if the list is empty?

What is the output when the linked list is empty (head is None) and the same traversal code runs?

DSA Python

head = None
current = head
while current:
    print(current.data, end=' -> ')
    current = current.next
print('null')

A null

B 0 -> null

C None -> null

D Error: AttributeError

💡 Hint

If head is None, does the loop run?

Since head is None, current is None, so the while loop does not run. Only 'null' is printed.

🔧 Debug

advanced

Identify the error in this linked list traversal code

What error does this code produce when run?

DSA Python

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

head = Node(1)
head.next = Node(2)

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

A Prints '1 -> 2 -> null'

B Prints '1 -> null'

C Prints '1 -> 2' without 'null'

D Prints '1 -> null' and misses last node data

💡 Hint

Check the loop condition and what nodes get printed.

The loop runs while current.next is not None, so it stops before the last node. The last node's data (2) is not printed, only '1 -> null' is printed.

🧠 Conceptual

advanced

How many nodes are printed by this traversal?

Given a linked list with 5 nodes, what is the number of nodes printed by this code?

DSA Python

current = head
count = 0
while current:
    print(current.data, end=' -> ')
    current = current.next
    count += 1
print('null')
print(count)

A 6

B 5

C 4

D 0

💡 Hint

The loop runs once per node until current is None.

The loop visits each of the 5 nodes exactly once, so count is 5.

🚀 Application

expert

What is the output after reversing and printing the linked list?

What is the printed output after reversing this linked list and then printing it?

DSA Python

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

def reverse(head):
    prev = None
    current = head
    while current:
        next_node = current.next
        current.next = prev
        prev = current
        current = next_node
    return prev

head = Node(1)
head.next = Node(2)
head.next.next = Node(3)

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

A null

B 1 -> 2 -> 3 -> null

C 3 -> 2 -> 1 -> null

D Error: infinite loop

💡 Hint

Reversing changes the direction of links between nodes.

The reverse function flips the list order. Printing after reversal shows nodes in reverse order: 3, 2, 1, then null.