Introduction

Insertion and deletion are the most important operations in a Linked List.

The task is to:

  • insert new nodes
  • delete existing nodes
  • maintain correct links between nodes

Example:

Input:1 -> 2 -> 4

Insert:
3

Output:
1 -> 2 -> 3 -> 4

Example:

Input:1 -> 2 -> 3 -> 4

Delete:
3

Output:
1 -> 2 -> 4

This problem is one of the most important basics of:

Linked List Data Structure

Constraints

 1 <= Number of Nodes <= 10^5-10^9 <= Node Value <= 10^9

Approach 1 : Brute Force (Using Array Conversion)

Explanations:

Explanation:

The idea is:

  • convert linked list into array
  • perform insert/delete operation
  • rebuild linked list

Steps:

  1. Traverse linked list.
  2. Store values into array.
  3. Insert/Delete value.
  4. Create new linked list.

This approach works but:

  • uses unnecessary extra space
  • rebuilding linked list is inefficient

So direct pointer manipulation is preferred.

Dry Run

Input:1 -> 2 -> 4

Insert:
3

Step 1:
Array:
[1,2,4]

Step 2:
Insert 3
Array:
[1,2,3,4]

Step 3:
Rebuild linked list

Output:
1 -> 2 -> 3 -> 4

Practice :

Complexity Analysis :

Time Complexity:- O(n)Explanation :
Linked list traversal is required.

Space Complexity:- O(n)
Explanation :
Extra array is used.

Approach 2 : Optimal Solution(Direct Pointer Manipulation)

Explanations:

Explanation:

This is the most optimized and interview-preferred solution.

The idea is:

  • directly manipulate node pointers
  • connect new node
  • bypass deleted node

This avoids extra space usage.

Dry Run

Input:1 -> 2 -> 4

Insert:
3 after 2

Step 1:
Create new node:
3

Step 2:
3.next = 4

Step 3:
2.next = 3

Output:
1 -> 2 -> 3 -> 4

Practice :

Complexity Analysis :

Time Complexity:- O(1)Explanation :
Insertion and deletion occur directly using pointers.

Space Complexity:- O(1)
Explanation :
No extra space is used.

Why This Problem is Important

This problem builds the foundation for:

  • Pointer manipulation
  • Dynamic memory handling
  • Linked List operations
  • Node connection logic
  • Data structure traversal

Real-World Applications

Insertion and deletion in linked lists are used in:

  • Browser history
  • Music playlists
  • Undo/Redo systems
  • Memory allocation
  • Dynamic scheduling systems

Common Beginner Mistakes

  • Losing node references
  • Incorrect pointer updates
  • Forgetting next connections
  • Breaking linked list structure
  • NULL pointer errors

Interview Tip

Interviewers often expect:

  • correct pointer manipulation
  • proper node insertion logic
  • clean deletion handling
  • O(1) operations

Always explain:

  • how pointers are reconnected
  • why linked lists support efficient insertion/deletion

Related Questions

  • Traverse Linked List
  • Search in Linked List
  • Reverse Linked List
  • Middle of Linked List
  • Detect Cycle in Linked List

Final Takeaway

The Insert/Delete Node problem is one of the most important beginner linked list problems.

It teaches:

  • pointer manipulation
  • node insertion
  • node deletion
  • dynamic structure updates

Understanding this problem builds a strong foundation for:

  •  advanced linked list algorithms
  • pointer-based problems
  • interview-level data structure questions.