Delete Node by Value in DSA C# - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after deleting a node by value?

Consider a singly linked list with nodes containing values 1 -> 2 -> 3 -> 4 -> null. We delete the node with value 3. What is the resulting list?

DSA C#

public class Node {
    public int Value;
    public Node Next;
    public Node(int value) { Value = value; Next = null; }
}

public class LinkedList {
    public Node Head;

    public void DeleteByValue(int value) {
        if (Head == null) return;
        if (Head.Value == value) {
            Head = Head.Next;
            return;
        }
        Node current = Head;
        while (current.Next != null && current.Next.Value != value) {
            current = current.Next;
        }
        if (current.Next != null) {
            current.Next = current.Next.Next;
        }
    }

    public override string ToString() {
        Node current = Head;
        string result = "";
        while (current != null) {
            result += current.Value + " -> ";
            current = current.Next;
        }
        return result + "null";
    }
}

LinkedList list = new LinkedList();
list.Head = new Node(1);
list.Head.Next = new Node(2);
list.Head.Next.Next = new Node(3);
list.Head.Next.Next.Next = new Node(4);
list.DeleteByValue(3);
Console.WriteLine(list.ToString());

A 1 -> 2 -> 4 -> null

B 1 -> 2 -> 3 -> 4 -> null

C 1 -> 3 -> 4 -> null

D 2 -> 3 -> 4 -> null

💡 Hint

Think about how the node with value 3 is removed and how the links are updated.

The node with value 3 is removed by linking the node with value 2 directly to the node with value 4, skipping the node with value 3.

❓ Predict Output

intermediate

What happens when deleting a non-existent value?

Given a linked list 5 -> 6 -> 7 -> null, what is the output after trying to delete the node with value 10?

DSA C#

public class Node {
    public int Value;
    public Node Next;
    public Node(int value) { Value = value; Next = null; }
}

public class LinkedList {
    public Node Head;

    public void DeleteByValue(int value) {
        if (Head == null) return;
        if (Head.Value == value) {
            Head = Head.Next;
            return;
        }
        Node current = Head;
        while (current.Next != null && current.Next.Value != value) {
            current = current.Next;
        }
        if (current.Next != null) {
            current.Next = current.Next.Next;
        }
    }

    public override string ToString() {
        Node current = Head;
        string result = "";
        while (current != null) {
            result += current.Value + " -> ";
            current = current.Next;
        }
        return result + "null";
    }
}

LinkedList list = new LinkedList();
list.Head = new Node(5);
list.Head.Next = new Node(6);
list.Head.Next.Next = new Node(7);
list.DeleteByValue(10);
Console.WriteLine(list.ToString());

A 5 -> 7 -> null

B 6 -> 7 -> null

C 5 -> 6 -> 7 -> null

D null

💡 Hint

If the value is not found, the list remains unchanged.

Since the value 10 is not in the list, no nodes are removed and the list stays the same.

❓ Predict Output

advanced

What is the output after deleting the head node by value?

Given a linked list 9 -> 8 -> 7 -> null, what is the output after deleting the node with value 9?

DSA C#

public class Node {
    public int Value;
    public Node Next;
    public Node(int value) { Value = value; Next = null; }
}

public class LinkedList {
    public Node Head;

    public void DeleteByValue(int value) {
        if (Head == null) return;
        if (Head.Value == value) {
            Head = Head.Next;
            return;
        }
        Node current = Head;
        while (current.Next != null && current.Next.Value != value) {
            current = current.Next;
        }
        if (current.Next != null) {
            current.Next = current.Next.Next;
        }
    }

    public override string ToString() {
        Node current = Head;
        string result = "";
        while (current != null) {
            result += current.Value + " -> ";
            current = current.Next;
        }
        return result + "null";
    }
}

LinkedList list = new LinkedList();
list.Head = new Node(9);
list.Head.Next = new Node(8);
list.Head.Next.Next = new Node(7);
list.DeleteByValue(9);
Console.WriteLine(list.ToString());

A 8 -> 7 -> null

B 7 -> null

C 9 -> 8 -> 7 -> null

D null

💡 Hint

Deleting the head means the head moves to the next node.

The head node with value 9 is removed, so the new head is the node with value 8.

🔧 Debug

advanced

Identify the error in this DeleteByValue method

What error will occur when running this DeleteByValue method on a linked list?

DSA C#

public void DeleteByValue(int value) {
    if (Head == null) return;
    Node current = Head;
    while (current.Next != null) {
        if (current.Next.Value == value) {
            current.Next = current.Next.Next;
            return;
        }
        current = current.Next;
    }
    if (Head.Value == value) {
        Head = Head.Next;
    }
}

A No error; deletes node correctly

B NullReferenceException when deleting head node

C Deletes only last node always

D Infinite loop occurs

💡 Hint

Check the order of checking head node and traversing nodes.

The method checks for the head node deletion after traversing, so if the head node matches, current.Next is null and accessing current.Next.Value causes NullReferenceException.

❓ Predict Output

expert

What is the output after deleting all nodes with a specific value?

Given a linked list 4 -> 5 -> 4 -> 6 -> 4 -> null, a method deletes all nodes with value 4. What is the resulting list?

DSA C#

public class Node {
    public int Value;
    public Node Next;
    public Node(int value) { Value = value; Next = null; }
}

public class LinkedList {
    public Node Head;

    public void DeleteAllByValue(int value) {
        while (Head != null && Head.Value == value) {
            Head = Head.Next;
        }
        Node current = Head;
        while (current != null && current.Next != null) {
            if (current.Next.Value == value) {
                current.Next = current.Next.Next;
            } else {
                current = current.Next;
            }
        }
    }

    public override string ToString() {
        Node current = Head;
        string result = "";
        while (current != null) {
            result += current.Value + " -> ";
            current = current.Next;
        }
        return result + "null";
    }
}

LinkedList list = new LinkedList();
list.Head = new Node(4);
list.Head.Next = new Node(5);
list.Head.Next.Next = new Node(4);
list.Head.Next.Next.Next = new Node(6);
list.Head.Next.Next.Next.Next = new Node(4);
list.DeleteAllByValue(4);
Console.WriteLine(list.ToString());

A null

B 4 -> 5 -> 6 -> null

C 5 -> 4 -> 6 -> null

D 5 -> 6 -> null

💡 Hint

All nodes with value 4 are removed, including head nodes.

All nodes with value 4 are removed, leaving only nodes with values 5 and 6.

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