Insert at Beginning Head Insert in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node and insert it at the beginning of the linked list.

DSA C

struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
new_node->data = data;
new_node->next = [1];
head = new_node;

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

Ahead

Bhead->next

CNULL

Dnew_node

Attempts:

3 left

💡 Hint

Common Mistakes

Setting new_node->next to NULL loses the rest of the list.

Setting new_node->next to new_node creates a cycle.

To insert at the beginning, the new node's next should point to the current head.

2fill in blank

medium

Complete the code to update the head pointer after inserting the new node at the beginning.

DSA C

new_node->next = head;
[1] = new_node;

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

Ahead

Bnew_node

Ctemp

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning head to temp or next causes errors.

Not updating head leaves the list unchanged.

After insertion, head should point to the new node.

3fill in blank

hard

Fix the error in the code that inserts a new node at the beginning of the list.

DSA C

struct Node* new_node = malloc(sizeof(struct Node));
new_node->data = data;
new_node->next = [1];
head = new_node;

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

Anew_node->next

Bhead->next

CNULL

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using head->next loses the first node.

Setting next to NULL breaks the chain.

The new node's next must point to the current head, not head->next or NULL.

4fill in blank

hard

Fill both blanks to correctly insert a new node at the beginning and update the head pointer.

DSA C

struct Node* new_node = malloc(sizeof(struct Node));
new_node->data = data;
new_node->next = [1];
[2] = new_node;

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

Ahead

Bnew_node

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of assignments.

Using wrong variable names.

The new node's next points to head, and head is updated to new_node.

5fill in blank

hard

Fill all three blanks to create a new node, link it at the beginning, and update the head pointer.

DSA C

struct Node* [1] = malloc(sizeof(struct Node));
[1]->data = data;
[1]->next = [2];
[3] = [1];

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

Anew_node

Bhead

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names.

Not updating head pointer.

Create new_node, set its next to head, then update head to new_node.

Practice

1. What does the "Insert at Beginning" operation do in a singly linked list?

easy

A. Deletes the first node of the list

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

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

D. Deletes the last node of the list

Solution

1. Step 1: Understand the operation

   Inserting at the beginning means placing a new node before the current first node.

2. Step 2: Effect on the list

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

3. Final Answer:

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

4. Quick Check:

   Insert at beginning = Add new head [OK]

Hint: New node becomes head, old head moves next [OK]

Common Mistakes:

• Confusing insert at beginning with insert at end
• Thinking it deletes nodes
• Assuming it inserts in the middle

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

easy

A. newNode->next = head; head = newNode;

B. head = newNode->next; newNode = head;

C. head->next = newNode; newNode = head;

D. newNode = head; head->next = newNode;

Solution

1. Step 1: Assign newNode's next to current head

   This links the new node to the existing list.

2. Step 2: Update head to newNode

   Now the new node is the first node in the list.

3. Final Answer:

   newNode->next = head; head = newNode; -> Option A

4. Quick Check:

   Link newNode to head, then update head [OK]

Hint: Point newNode->next to head, then head to newNode [OK]

Common Mistakes:

• Swapping assignments order
• Assigning head to newNode->next incorrectly
• Not updating head pointer

3. What will be the linked list after inserting nodes with values 10, then 20, then 30 at the beginning in that order? Assume the list was initially empty.

medium

A. 10 -> 20 -> 30 -> null

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

C. 20 -> 30 -> 10 -> null

D. 30 -> 20 -> 10 -> null

Solution

1. Step 1: Insert 10 at beginning

   List becomes 10 -> null.

2. Step 2: Insert 20 at beginning

   List becomes 20 -> 10 -> null.

3. Step 3: Insert 30 at beginning

   List becomes 30 -> 20 -> 10 -> null.

4. Final Answer:

   30 -> 20 -> 10 -> null -> Option D

5. Quick Check:

   Last inserted is new head [OK]

Hint: Last inserted node is always head [OK]

Common Mistakes:

• Assuming insertion at end
• Reversing insertion order
• Confusing node values order

4. Given the following code snippet, what is the error that prevents correct insertion at the beginning?

struct Node {
  int data;
  struct Node* next;
};

void insertAtBeginning(struct Node** head, int val) {
  struct Node* newNode = malloc(sizeof(struct Node));
  newNode->data = val;
  newNode->next = NULL;
  *head = newNode;
}

medium

A. malloc size is incorrect

B. newNode->next should point to current head before updating head

C. newNode->data is not assigned

D. head pointer should not be double pointer

Solution

1. Step 1: Check newNode->next assignment

   It is set to NULL, losing the existing list.

2. Step 2: Correct linking

   newNode->next should point to current head before head is updated.

3. Final Answer:

   newNode->next should point to current head before updating head -> Option B

4. Quick Check:

   Link newNode->next to old head before head update [OK]

Hint: Link newNode->next to old head before head update [OK]

Common Mistakes:

• Setting newNode->next to NULL always
• Not using double pointer for head
• Forgetting to assign data

5. You have a singly linked list with nodes: 5 -> 15 -> 25 -> null. You want to insert a new node with value 10 at the beginning. After insertion, what will be the correct sequence of nodes?

hard

A. 10 -> 5 -> 15 -> 25 -> null

B. 5 -> 10 -> 15 -> 25 -> null

C. 10 -> 15 -> 25 -> 5 -> null

D. 5 -> 15 -> 25 -> 10 -> null

Solution

1. Step 1: Current list is 5 -> 15 -> 25 -> null

   This is the starting list before insertion.

2. Step 2: Insert 10 at beginning

   New node 10 points to current head (5), then head updated to 10.

3. Final Answer:

   10 -> 5 -> 15 -> 25 -> null -> Option A

4. Quick Check:

   New node becomes head, old head follows [OK]

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

Common Mistakes:

• Inserting at wrong position
• Not updating head pointer
• Linking nodes incorrectly