🔍 DSA Interview Q&A – Day 1: Arrays vs Linked Lists

Welcome to Day 1 of the DSA Interview Q&A Series, where we dive deep into commonly asked data structures and algorithms questions to help you prepare smarter for technical interviews.

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✅ Question

What is the difference between an Array and a Linked List?

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💡 Answer

Arrays and Linked Lists are both linear data structures, but they differ in how they handle memory, operations, and performance.

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🔸 Array

Feature	Description
Memory	Contiguous block of memory
Size	Fixed size (defined at creation)
Access Time	O(1) – Direct access via index
Insertion	O(n) – Elements must shift
Deletion	O(n) – Elements must shift

Use Case: Best when you need fast, direct access and the size of data doesn't change frequently.

Example (C#):

int[] arr = { 10, 20, 30, 40, 50 };
Console.WriteLine(arr[2]); // Output: 30

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🔸 Linked List

Feature	Description
Memory	Nodes are scattered in memory; each node points to the next
Size	Dynamic – grows/shrinks as needed
Access Time	O(n) – Must traverse from head
Insertion	O(1) – If pointer to node is known
Deletion	O(1) – If pointer to node is known

Use Case: Ideal when frequent insertions and deletions are required and random access is not needed.

Example (C#):

public class Node
{
    public int Data;
    public Node Next;
}

Node head = new Node { Data = 10, Next = null };
head.Next = new Node { Data = 20, Next = null };

Console.WriteLine(head.Next.Data); // Output: 20

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🧠 Key Comparison

Feature	Array	Linked List
Memory Layout	Contiguous	Non-contiguous
Size Flexibility	Fixed	Dynamic
Access	O(1)	O(n)
Insertion	O(n)	O(1)*
Deletion	O(n)	O(1)*

*If pointer/reference to the node is already known.

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🎯 Interview Tip

• Prefer arrays when you need fast indexing and minimal insert/delete operations.
• Use linked lists when your program needs frequent modifications (insert/delete) in the middle of the structure.

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👉 Up Next: How to detect a cycle in a linked list (Floyd’s Algorithm)

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💬 Comment below your experience or tips using arrays and linked lists in projects.