Get Length of Linked List in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the length counter to zero.

DSA Python

def get_length(head):
    length = [1]
    current = head
    while current:
        length += 1
        current = current.next
    return length

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

A0

B1

Chead

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Starting length at 1 instead of 0

Setting length to None

Assigning length to head

We start counting from zero because the list might be empty.

2fill in blank

medium

Complete the code to move to the next node in the linked list.

DSA Python

def get_length(head):
    length = 0
    current = head
    while current:
        length += 1
        current = [1]
    return length

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

Ahead.next

Bcurrent

Ccurrent.next

Dlength.next

Attempts:

3 left

💡 Hint

Common Mistakes

Using head.next instead of current.next

Assigning current to itself causing infinite loop

Using length.next which is invalid

To move forward, we assign current to the next node.

3fill in blank

hard

Fix the error in the loop condition to correctly check if the current node exists.

DSA Python

def get_length(head):
    length = 0
    current = head
    while [1]:
        length += 1
        current = current.next
    return length

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

Acurrent == None

Bcurrent is not None

Chead

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'current == None' which is less preferred

Using 'head' which does not change in the loop

Using 'length' which is an integer

The loop should continue while current is not None.

4fill in blank

hard

Fill both blanks to create a dictionary with word lengths for words longer than 3 characters.

DSA Python

words = ['apple', 'bat', 'carrot', 'dog']
lengths = {word: [1] for word in words if len(word) [2] 3}

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

Alen(word)

B>

C<

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>'

Using 'word' instead of 'len(word)'

Not filtering words by length

We want the length of each word and only include words longer than 3 characters.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase keys and values greater than zero.

DSA Python

data = {'a': 1, 'b': 0, 'c': 3}
result = [1]: [2] for k, v in data.items() if v [3] 0}

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

Ak.upper()

Bv

C>

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'k' instead of 'k.upper()' for keys

Using '<' instead of '>' for filtering

Including values equal to zero

Keys are converted to uppercase, values are included if greater than zero.

Practice

1. What does the length of a linked list represent?

easy

A. The memory size of the linked list

B. The value of the first node

C. The number of nodes in the linked list

D. The value of the last node

Solution

1. Step 1: Understand linked list structure

   A linked list is made of nodes connected one after another.

2. Step 2: Define length meaning

   The length is how many nodes are present in the list.

3. Final Answer:

   The number of nodes in the linked list -> Option C

4. Quick Check:

   Length counts nodes = number of nodes [OK]

Hint: Length = count of nodes from head to end [OK]

Common Mistakes:

• Confusing length with node values
• Thinking length is memory size
• Counting only first or last node

2. Which of the following Python code snippets correctly initializes a variable to count the length of a linked list?

easy

A. length = None

B. length = 0

C. length = head

D. length = []

Solution

1. Step 1: Identify counting variable type

   Length should be a number starting at zero before counting nodes.

2. Step 2: Check each option

   length = 0 sets length to 0, ready to increment. Others assign wrong types.

3. Final Answer:

   length = 0 -> Option B

4. Quick Check:

   Initialize count as 0 before loop [OK]

Hint: Start counting length from zero [OK]

Common Mistakes:

• Initializing length as None or list
• Assigning length to head node
• Using wrong data types for count

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

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

def get_length(head):
    count = 0
    current = head
    while current:
        count += 1
        current = current.next
    return count

# Creating linked list: 10 -> 20 -> 30 -> None
head = Node(10)
head.next = Node(20)
head.next.next = Node(30)

print(get_length(head))

medium

A. 3

B. 2

C. 0

D. None

Solution

1. Step 1: Trace linked list nodes

   List has nodes with values 10, 20, and 30, total 3 nodes.

2. Step 2: Follow get_length function

   Function counts nodes by moving current pointer until None, increments count each step.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Count nodes 10,20,30 = 3 [OK]

Hint: Count nodes by traversing until None [OK]

Common Mistakes:

• Stopping count early
• Not incrementing count inside loop
• Returning None instead of count

4. Find the error in this code to get the length of a linked list:

def get_length(head):
    count = 0
    while head.next:
        count += 1
        head = head.next
    return count

medium

A. It misses counting the last node

B. It causes infinite loop

C. It returns None instead of count

D. It counts nodes twice

Solution

1. Step 1: Analyze loop condition

   Loop runs while head.next exists, so it stops before last node.

2. Step 2: Check counting logic

   Last node is not counted because loop ends early, count misses one node.

3. Final Answer:

   It misses counting the last node -> Option A

4. Quick Check:

   Loop condition excludes last node [OK]

Hint: Use 'while current' not 'while current.next' to count all nodes [OK]

Common Mistakes:

• Using head.next in loop condition
• Not counting last node
• Assuming loop covers all nodes

5. You have a linked list where each node contains a number. Write a function to find the length of the linked list only if all node values are positive. If any node has zero or negative value, return 0 immediately. What is the correct approach?

hard

A. Check only first node value, then count all nodes

B. Count nodes first, then check values in a second pass

C. Return length without checking values

D. Traverse nodes, if value <= 0 return 0, else count nodes till end

Solution

1. Step 1: Traverse and check values simultaneously

   Move through each node, check if value is positive.

2. Step 2: Return 0 immediately if value is zero or negative, else keep counting

   If any node fails condition, stop and return 0; otherwise, return total count.

3. Final Answer:

   Traverse nodes, if value <= 0 return 0, else count nodes till end -> Option D

4. Quick Check:

   Check values while counting, stop early if invalid [OK]

Hint: Check values during traversal, stop early if invalid [OK]

Common Mistakes:

• Counting first, then checking values
• Ignoring node values
• Checking only first node value