Delete Node by Value in DSA Typescript - Time & Space Complexity

Time Complexity: Delete Node by Value

O(n)

Understanding Time Complexity

When we delete a node by value from a linked list, we want to know how long it takes as the list grows.

We ask: How does the time to find and remove the node change with list size?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

function deleteNode(head: ListNode | null, value: number): ListNode | null {
  if (!head) return null;
  if (head.val === value) return head.next;
  let current = head;
  while (current.next && current.next.val !== value) {
    current = current.next;
  }
  if (current.next) {
    current.next = current.next.next;
  }
  return head;
}
    

This code searches the linked list for the first node with the given value and removes it by changing pointers.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The while loop that moves through the list nodes one by one.
• How many times: Up to once for each node until the value is found or the list ends.

How Execution Grows With Input

As the list gets longer, the search may take more steps because it checks nodes one by one.

Input Size (n)	Approx. Operations
10	Up to 10 checks
100	Up to 100 checks
1000	Up to 1000 checks

Pattern observation: The number of steps grows roughly in direct proportion to the list size.

Final Time Complexity

Time Complexity: O(n)

This means the time to delete a node grows linearly with the number of nodes in the list.

Common Mistake

[X] Wrong: "Deleting a node by value always takes constant time because we just change pointers."

[OK] Correct: We must first find the node by checking nodes one by one, which takes time proportional to the list size.

Interview Connect

Understanding this helps you explain how searching affects deletion speed in linked lists, a common topic in coding discussions.

Self-Check

"What if the list was doubly linked? How would the time complexity change when deleting a node by value?"

Practice

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

easy

A. Reverse the linked list

B. Add a new node with the given value at the end

C. Remove the first node that contains the given value

D. Find the position of a node with the given value

Solution

1. Step 1: Understand the operation goal

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

2. Step 2: Identify the correct action

   Removing the first node with the given value means deleting that node and linking its previous node to the next node.

3. Final Answer:

   Remove the first node that contains the given value -> Option C

4. Quick Check:

   Delete node by value = Remove first matching node [OK]

Hint: Delete node by value means remove first matching node [OK]

Common Mistakes:

• Confusing deletion with insertion
• Trying to delete all nodes with the value instead of first
• Thinking it finds position only
• Assuming it reverses the list

2. Which of the following TypeScript code snippets correctly deletes the head node if its value is 5 from a singly linked list starting at head?

easy

A. if (head.value === 5) head = head.next;

B. head = head.next.value === 5 ? head.next.next : head;

C. while (head.value !== 5) head = head.next;

D. head.next = null;

Solution

1. Step 1: Check if head node has value 5

   If the first node's value is 5, we remove it by moving head to the next node.

2. Step 2: Verify code correctness

   if (head.value === 5) head = head.next; correctly updates head to head.next if head.value is 5, effectively deleting the first node.

3. Final Answer:

   if (head.value === 5) head = head.next; -> Option A

4. Quick Check:

   Delete head node by reassigning head [OK]

Hint: Check head value first, then update head pointer [OK]

Common Mistakes:

• Using incorrect conditional expressions
• Assigning head.next incorrectly
• Not handling head node deletion
• Overwriting head without checks

3. Given the linked list: 1 -> 3 -> 5 -> 7 -> null, what is the list after deleting the node with value 5 using the following TypeScript code?

let current = head;
while (current.next !== null) {
  if (current.next.value === 5) {
    current.next = current.next.next;
    break;
  }
  current = current.next;
}

medium

A. 1 -> 3 -> 5 -> 7 -> null

B. 1 -> 3 -> 7 -> null

C. 3 -> 5 -> 7 -> null

D. 1 -> 7 -> null

Solution

1. Step 1: Traverse list to find node before value 5

   Loop checks nodes until current.next.value is 5, which is true when current is node with value 3.

2. Step 2: Delete node with value 5 by skipping it

   Set current.next to current.next.next, linking node 3 directly to node 7, removing node 5.

3. Final Answer:

   1 -> 3 -> 7 -> null -> Option B

4. Quick Check:

   Skip node with value 5 = 1->3->7 [OK]

Hint: Skip node by linking previous to next [OK]

Common Mistakes:

• Not breaking loop after deletion
• Deleting wrong node
• Not updating pointers correctly
• Confusing current and current.next

4. Consider this buggy TypeScript code to delete a node by value from a singly linked list:

function deleteNode(head: Node | null, value: number): Node | null {
  let current = head;
  while (current !== null) {
    if (current.next?.value === value) {
      current.next = current.next.next;
    }
    current = current.next!;
  }
  return head;
}

What is the main problem with this code?

medium

A. It may cause a runtime error when current.next is null

B. It deletes all nodes with the value instead of the first

C. It does not handle deletion if head node has the value

D. It reverses the linked list accidentally

Solution

1. Step 1: Analyze the loop termination

   The while (current !== null) continues to the last node where current.next is null. The if uses ?. safely, but then executes current = current.next!;, and ! non-null assertion on null causes runtime error.

2. Step 2: Confirm the bug triggers always

   For any non-empty list, it crashes at the last node regardless of value, preventing correct execution.

3. Final Answer:

   It may cause a runtime error when current.next is null -> Option A

4. Quick Check:

   current.next! on null = runtime error [OK]

Hint: Beware of non-null assertion ! on potentially null next [OK]

Common Mistakes:

• Using non-null assertion (!) on potentially null next
• Assuming current.next always exists
• Not breaking after deletion
• Confusing current and current.next updates

5. You have a singly linked list: 2 -> 4 -> 6 -> 4 -> 8 -> null. You want to delete the first node with value 4. After deletion, you want to insert a new node with value 10 right after the deleted node's position. Which sequence of operations correctly achieves this?

hard

A. Delete first 4, then insert 10 after node 6

B. Insert 10 at head, then delete first 4

C. Delete all 4s, then insert 10 at end

D. Delete first 4, then insert 10 after node 2

Solution

1. Step 1: Delete first node with value 4

   The first 4 is the second node, so remove it by linking node 2 to node 6.

2. Step 2: Insert new node with value 10 after node 2

   Create new node 10 and link it after node 2, then link new node to node 6.

3. Final Answer:

   Delete first 4, then insert 10 after node 2 -> Option D

4. Quick Check:

   Delete 4, insert 10 after previous node [OK]

Hint: Delete node, then insert new node at same position [OK]

Common Mistakes:

• Inserting new node at wrong position
• Deleting all nodes with value 4
• Not updating links correctly
• Inserting before deletion