Delete Node by Value in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the list is empty before deletion.

DSA C

if (head == [1]) {
    printf("List is empty.\n");
    return head;
}

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

ANULL

B0

Chead

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 instead of NULL for pointer comparison.

Checking if head equals 1 or head itself.

We check if head is NULL to know if the list is empty.

2fill in blank

medium

Complete the code to delete the head node when it matches the value.

DSA C

if (head->data == value) {
    struct Node* temp = head;
    head = head->[1];
    free(temp);
    return head;
}

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

Aprev

Bnext

Cvalue

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using head->prev which does not exist in singly linked list.

Using head->data or head->value which are data fields, not pointers.

To delete the head node, we move head to head->next.

3fill in blank

hard

Fix the error in the loop condition to find the node before the one to delete.

DSA C

while (current->next != NULL && current->next->data [1] value) {
    current = current->next;
}

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

A!=

B==

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' causes loop to stop immediately if first node matches.

Using '>' or '<' is incorrect for equality check.

We continue while current->next->data is not equal to value to find the node before target.

4fill in blank

hard

Fill both blanks to correctly remove the target node from the list.

DSA C

if (current->next != NULL) {
    struct Node* temp = current->[1];
    current->[2] = temp->next;
    free(temp);
}

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

Anext

Bprev

Cdata

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using prev which does not exist in singly linked list.

Using data or value which are data fields, not pointers.

We use current->next to access and remove the target node.

5fill in blank

hard

Fill all three blanks to complete the delete function returning the updated head.

DSA C

struct Node* deleteNode(struct Node* head, int value) {
    struct Node* current = head;
    if (head == [1]) return head;
    if (head->data == value) {
        struct Node* temp = head;
        head = head->[2];
        free(temp);
        return head;
    }
    while (current->next != NULL && current->next->data != value) {
        current = current->next;
    }
    if (current->next != NULL) {
        struct Node* temp = current->next;
        current->next = temp->[3];
        free(temp);
    }
    return head;
}

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

ANULL

Bnext

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using prev pointer which does not exist in singly linked list.

Not updating head when deleting the first node.

Check for empty list with NULL, move head to head->next, and link current->next to temp->next.

Practice

1. What is the main purpose of the Delete Node by Value operation in a linked list?

easy

A. To remove the first node that contains the given value from the list

B. To add a new node with the given value at the end of the list

C. To find the position of a node with the given value

D. To reverse the linked list

Solution

1. Step 1: Understand the operation's goal

   The operation aims to remove a node that matches a specific value from the linked list.

2. Step 2: Identify the correct description

   Removing the first node with the given value matches To remove the first node that contains the given value from the list, while others describe different operations.

3. Final Answer:

   To remove the first node that contains the given value from the list -> Option A

4. Quick Check:

   Delete Node by Value = Remove matching node [OK]

Hint: Deleting by value means removing the first matching node [OK]

Common Mistakes:

• Confusing deletion by value with insertion
• Thinking it reverses the list
• Assuming it finds position only

2. Which of the following is the correct way to start deleting a node by value in a singly linked list in C?

easy

A. Reverse the list before deletion

B. Directly free the head pointer without checks

C. Create a new node with the value to delete

D. Set a pointer to the head and check if head's value matches

Solution

1. Step 1: Understand deletion start

   We must check if the head node itself contains the value to delete before moving forward.

2. Step 2: Identify correct approach

   Setting a pointer to head and checking its value is the correct first step; other options are incorrect or irrelevant.

3. Final Answer:

   Set a pointer to the head and check if head's value matches -> Option D

4. Quick Check:

   Start at head to delete by value [OK]

Hint: Always check head node first when deleting by value [OK]

Common Mistakes:

• Freeing head without checking value
• Creating new nodes unnecessarily
• Reversing list before deletion

3. Consider the following linked list: 10 -> 20 -> 30 -> 40 -> NULL. After deleting the node with value 30, what will be the new list?

medium

A. 10 -> 30 -> 40 -> NULL

B. 10 -> 20 -> 40 -> NULL

C. 20 -> 30 -> 40 -> NULL

D. 10 -> 20 -> 30 -> 40 -> NULL

Solution

1. Step 1: Locate node with value 30

   Traverse the list: 10, 20, then 30 is found as the third node.

2. Step 2: Remove node 30 and link previous to next

   Link node with value 20 directly to node with value 40, skipping 30.

3. Final Answer:

   10 -> 20 -> 40 -> NULL -> Option B

4. Quick Check:

   Deleted 30, list skips it [OK]

Hint: Link previous node to next to remove target node [OK]

Common Mistakes:

• Not updating previous node's next pointer
• Deleting wrong node
• Leaving deleted node in list

4. Given this code snippet to delete a node by value, what is the main error?

void deleteNode(Node** head, int val) {
  Node* temp = *head;
  Node* prev = NULL;
  while (temp != NULL && temp->data != val) {
    prev = temp;
    temp = temp->next;
  }
  free(temp);
  if (prev != NULL) {
    prev->next = temp->next;
  } else {
    *head = temp->next;
  }
}

medium

A. prev pointer is never updated

B. The loop condition is incorrect and never runs

C. free(temp) is called before updating pointers, causing invalid access

D. The function does not handle empty list

Solution

1. Step 1: Analyze order of free and pointer update

   The code frees temp before updating prev->next or head, so temp->next access is invalid.

2. Step 2: Identify correct fix

   Pointers must be updated before freeing the node to avoid accessing freed memory.

3. Final Answer:

   free(temp) is called before updating pointers, causing invalid access -> Option C

4. Quick Check:

   Free after pointer update to avoid errors [OK]

Hint: Update pointers before freeing node to avoid invalid access [OK]

Common Mistakes:

• Freeing node before fixing links
• Ignoring NULL list case
• Not updating prev pointer

5. You have a singly linked list: 5 -> 10 -> 15 -> 20 -> 25 -> NULL. Write a function to delete all nodes with value greater than 15. What will be the final list after deletion?

hard

A. 5 -> 10 -> 15 -> NULL

B. 5 -> 10 -> 20 -> 25 -> NULL

C. 15 -> 20 -> 25 -> NULL

D. 5 -> 10 -> 15 -> 20 -> 25 -> NULL

Solution

1. Step 1: Identify nodes with value > 15

   Nodes with values 20 and 25 are greater than 15 and must be deleted.

2. Step 2: Delete nodes and link remaining nodes

   After removing 20 and 25, the list becomes 5 -> 10 -> 15 -> NULL.

3. Final Answer:

   5 -> 10 -> 15 -> NULL -> Option A

4. Quick Check:

   Removed nodes > 15, list ends at 15 [OK]

Hint: Delete nodes by checking value > 15 and relink list [OK]

Common Mistakes:

• Deleting wrong nodes
• Not updating links after deletion
• Assuming only one node deleted