Insert at Beginning Head Insert in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with the given data.

DSA Python

new_node = Node([1])

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

Ahead

BNone

Cdata

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'head' instead of 'data' when creating the new node.

Passing 'None' or 'next' instead of the data value.

We create a new node by passing the data value to the Node constructor.

2fill in blank

medium

Complete the code to link the new node to the current head of the list.

DSA Python

new_node.next = [1]

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

Ahead

BNone

Cdata

Dnew_node

Attempts:

3 left

💡 Hint

Common Mistakes

Setting new_node.next to itself.

Setting new_node.next to None or data.

The new node's next pointer should point to the current head node.

3fill in blank

hard

Fix the error in updating the head pointer to the new node.

DSA Python

head = [1]

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

Adata

BNone

Chead.next

Dnew_node

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning head to data or None instead of new_node.

Assigning head to head.next which skips the new node.

After insertion, the head should point to the new node.

4fill in blank

hard

Fill both blanks to complete the function that inserts a new node at the beginning.

DSA Python

def insert_at_beginning(head, [1]):
    new_node = Node(data)
    new_node.next = [2]
    head = new_node
    return head

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

Adata

Bhead.next

Chead

Dnew_node

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'head.next' instead of 'head' for new_node.next.

Using 'new_node' as a parameter instead of 'data'.

The function takes 'data' as input and links new_node.next to current head.

5fill in blank

hard

Fill all three blanks to complete the full insert at beginning function with Node class.

DSA Python

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

def insert_at_beginning([1], [2]):
    new_node = Node(data)
    new_node.next = [3]
    head = new_node
    return head

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

Ahead

Bdata

Dnew_node

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping parameter order or names.

Setting new_node.next to new_node instead of head.

The function takes head and data, links new_node.next to head, and returns new_node as new head.

Practice

1. What does the operation insert at beginning do in a linked list?

easy

A. Deletes the first node of the list

B. Adds a new node at the start of the list

C. Adds a new node at the end of the list

D. Deletes the last node of the list

Solution

1. Step 1: Understand the meaning of 'insert at beginning'

   Inserting at the beginning means adding a new element before the current first element.

2. Step 2: Identify the effect on the linked list

   The new node becomes the new head, pushing the old head to second position.

3. Final Answer:

   Adds a new node at the start of the list -> Option B

4. Quick Check:

   Insert at beginning = Add new head [OK]

Hint: Insert at beginning means new head node [OK]

Common Mistakes:

• Confusing insert at beginning with insert at end
• Thinking it deletes nodes instead of adding
• Assuming it changes the last node

2. Which of the following is the correct syntax to insert a new node at the beginning of a singly linked list in Python?

easy

A. new_node = head.next; head = new_node

B. head.next = new_node; new_node = head

C. head = head.next; new_node = head

D. new_node.next = head; head = new_node

Solution

1. Step 1: Understand pointer assignment for head insert

   To insert at beginning, new_node's next points to current head.

2. Step 2: Update head to new_node

   Then head is updated to new_node to make it the first node.

3. Final Answer:

   new_node.next = head; head = new_node -> Option D

4. Quick Check:

   Set new_node.next to head, then head = new_node [OK]

Hint: Link new node to head, then update head [OK]

Common Mistakes:

• Assigning head.next instead of new_node.next
• Not updating head to new_node
• Swapping assignment order incorrectly

3. What will be the linked list after executing the following code?

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

head = Node(10)
new_node = Node(20)
new_node.next = head
head = new_node

medium

A. 20 -> 10 -> null

B. 10 -> 20 -> null

C. 20 -> null

D. 10 -> null

Solution

1. Step 1: Create initial list with head node 10

   Initially, head points to node with data 10 and next is None.

2. Step 2: Insert new_node with data 20 at beginning

   new_node.next points to head (node 10), then head updated to new_node.

3. Final Answer:

   20 -> 10 -> null -> Option A

4. Quick Check:

   New node 20 becomes head, points to 10 [OK]

Hint: New node points to old head, then becomes head [OK]

Common Mistakes:

• Thinking new_node is added at end
• Not updating head to new_node
• Confusing node data order

4. Identify the error in this code snippet that tries to insert a node at the beginning of a linked list:

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

head = Node(5)
new_node = Node(15)
head = new_node
new_node.next = head

medium

A. The order of assignments is wrong; new_node.next should be set before head update

B. Node class is missing a data attribute

C. head should be None initially

D. new_node should not be created before head

Solution

1. Step 1: Analyze assignment order

   head is set to new_node first, then new_node.next is set to head (which is now new_node itself).

2. Step 2: Identify logical error

   This causes new_node.next to point to itself, losing original list starting at old head.

3. Final Answer:

   The order of assignments is wrong; new_node.next should be set before head update -> Option A

4. Quick Check:

   Set new_node.next before head = new_node [OK]

Hint: Set new_node.next before updating head [OK]

Common Mistakes:

• Updating head before linking new_node.next
• Confusing attribute initialization
• Assuming head must be None initially

5. Given a linked list with nodes containing values [30, 20, 10] (30 is head), which sequence of operations correctly inserts a new node with value 40 at the beginning and results in the list 40 -> 30 -> 20 -> 10 -> null?

hard

A. new_node = Node(40); new_node.next = None; head = new_node

B. new_node = Node(40); head.next = new_node; head = new_node

C. new_node = Node(40); new_node.next = head; head = new_node

D. new_node = Node(40); head = new_node; new_node.next = head

Solution

1. Step 1: Create new node with value 40

   new_node is created with data 40 and next initially None.

2. Step 2: Link new_node to current head

   Set new_node.next to current head (node 30) to keep existing list after new node.

3. Step 3: Update head to new_node

   Head pointer is updated to new_node, making it the first node.

4. Final Answer:

   new_node = Node(40); new_node.next = head; head = new_node -> Option C

5. Quick Check:

   Link new node to old head, then update head [OK]

Hint: Link new node to head, then update head pointer [OK]

Common Mistakes:

• Linking head.next instead of new_node.next
• Updating head before linking new_node.next
• Setting new_node.next to None losing list