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 deleting a node.

DSA C#

if (head == [1]) {
    return;
}

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

Anull

B0

Chead

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 instead of null to check for empty list.

Checking head itself instead of null.

We check if head is null to know if the list is empty before deleting.

2fill in blank

medium

Complete the code to delete the head node if it contains the target value.

DSA C#

if (head.Value == [1]) {
    head = head.Next;
    return;
}

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

Atarget

Bvalue

Chead

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with head instead of target.

Using null instead of target.

We compare head's value with the target to delete the first node if it matches.

3fill in blank

hard

Fix the error in the while loop condition to traverse the list correctly.

DSA C#

while (current.Next != [1] && current.Next.Value != target) {
    current = current.Next;
}

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

Acurrent

Bnull

Ctarget

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of null in condition.

Comparing current.Next to target directly.

We check current.Next != null to avoid null reference and continue traversal.

4fill in blank

hard

Fill both blanks to remove the node with the target value from the list.

DSA C#

if (current.Next != [1]) {
    current.Next = current.Next.[2];
}

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

Anull

BNext

CPrevious

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using Previous instead of Next.

Checking against head instead of null.

We check current.Next is not null, then link current.Next to the next node after the one to delete.

5fill in blank

hard

Fill all three blanks to complete the DeleteNodeByValue method.

DSA C#

public void DeleteNodeByValue(int target) {
    if (head == [1]) return;
    if (head.Value == target) {
        head = head.[2];
        return;
    }
    Node current = head;
    while (current.Next != [3] && current.Next.Value != target) {
        current = current.Next;
    }
    if (current.Next != null) {
        current.Next = current.Next.Next;
    }
}

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

Anull

BNext

Chead

DPrevious

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of null in conditions.

Using Previous instead of Next for node links.

We check if head is null, then update head to head.Next if first node matches target, and traverse until current.Next is null or matches target.

Practice

1. What does the operation Delete Node by Value do in a linked list?

easy

A. Adds a new node with the given value at the end of the list

B. Finds the node with the given value and returns it without removing

C. Removes the first node that contains the given value from the list

D. Reverses the linked list

Solution

1. Step 1: Understand the operation

   Deleting a node by value means searching for the first node that matches the value and removing it from the linked list.

2. Step 2: Compare options

   Only Removes the first node that contains the given value from the list describes removing the first node with the given value. Others describe adding, finding without removing, or reversing, which are different operations.

3. Final Answer:

   Removes the first node that contains the given value from the list -> Option C

4. Quick Check:

   Delete Node by Value = Remove first matching node [OK]

Hint: Deleting by value removes first matching node only [OK]

Common Mistakes:

• Confusing deletion by value with adding a node
• Thinking it removes all nodes with that value
• Assuming it reverses the list

2. Which of the following is the correct C# syntax to delete a node by value from a singly linked list?

easy

A. void DeleteNodeByValue(int value) { /* code */ }

B. public void DeleteNode(int value) { /* code */ }

C. public int DeleteNode(int value) { /* code */ }

D. DeleteNode(int value) => { /* code */ }

Solution

1. Step 1: Check method signature conventions in C#

   In C#, methods usually have an access modifier like 'public' and a return type. Deleting a node usually returns void.

2. Step 2: Analyze options

   public void DeleteNode(int value) { /* code */ } uses 'public void DeleteNode(int value)', which is correct. void DeleteNodeByValue(int value) { /* code */ } misses access modifier. public int DeleteNode(int value) { /* code */ } returns int which is uncommon here. DeleteNode(int value) => { /* code */ } uses invalid lambda syntax for method.

3. Final Answer:

   public void DeleteNode(int value) { /* code */ } -> Option B

4. Quick Check:

   Correct method signature = public void DeleteNode(int value) { /* code */ } [OK]

Hint: Use public void method with parameter for deletion [OK]

Common Mistakes:

• Omitting access modifier
• Using wrong return type
• Incorrect method syntax

3. Given the linked list: 10 -> 20 -> 30 -> 40 -> null, what is the list after deleting the node with value 30 using the DeleteNodeByValue method?

medium

A. 10 -> 20 -> 40 -> null

B. 10 -> 20 -> 30 -> 40 -> null

C. 20 -> 30 -> 40 -> null

D. 10 -> 30 -> 40 -> null

Solution

1. Step 1: Identify the node to delete

   The node with value 30 is the third node in the list.

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

   After deleting 30, the node with value 20 points directly to 40, so the list becomes 10 -> 20 -> 40 -> null.

3. Final Answer:

   10 -> 20 -> 40 -> null -> Option A

4. Quick Check:

   Deleted 30, list skips it [OK]

Hint: Remove node and link previous to next node [OK]

Common Mistakes:

• Not updating links after deletion
• Deleting wrong node
• Leaving deleted node in list

4. Consider this code snippet to delete a node by value in a singly linked list:

public void DeleteNode(int value) {
  Node current = head;
  Node previous = null;
  while (current != null && current.data != value) {
    previous = current;
    current = current.next;
  }
  if (current == null) return;
  previous.next = current.next;
}

What error will occur when deleting the head node?

medium

A. Compilation error due to missing return type

B. No error, deletion works fine

C. Infinite loop because current never changes

D. NullReferenceException because previous is null when deleting head

Solution

1. Step 1: Analyze deletion of head node

   If the node to delete is head, previous is still null because loop never runs.

2. Step 2: Check assignment previous.next = current.next

   Since previous is null, trying to access previous.next causes NullReferenceException.

3. Final Answer:

   NullReferenceException because previous is null when deleting head -> Option D

4. Quick Check:

   Deleting head needs special case to avoid null error [OK]

Hint: Handle head deletion separately to avoid null errors [OK]

Common Mistakes:

• Not checking if node to delete is head
• Assuming previous is never null
• Ignoring null pointer exceptions

5. You have a singly linked list: 5 -> 10 -> 15 -> 20 -> 25 -> null. You want to delete the node with value 5 (head), then delete the node with value 20. What will the list look like after these two deletions?

hard

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

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

C. 10 -> 15 -> 20 -> 25 -> null

D. 15 -> 25 -> null

Solution

1. Step 1: Delete head node with value 5

   Removing head means head moves to next node, so list becomes 10 -> 15 -> 20 -> 25 -> null.

2. Step 2: Delete node with value 20

   Find node 20 and remove it by linking 15 to 25, resulting in 10 -> 15 -> 25 -> null.

3. Final Answer:

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

4. Quick Check:

   Deleted head and middle node correctly [OK]

Hint: Delete head first, then link previous to next for others [OK]

Common Mistakes:

• Not updating head after deleting first node
• Not linking nodes correctly after deletion
• Deleting wrong nodes