🧱 1. What is a Linked List?

A Linked List is a linear data structure where elements are stored in nodes , and each node points to the next.

[value | next] → [value | next] → [value | null]

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👉 Last node always points to null

🔧 2. Node Structure

function Node ( value ) { this . data = value ; this . next = null ; }

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🏗️ 3. Linked List Class

var MyLinkedList = function () { this . head = null ; this . len = 0 ; // MUST be 0 };

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⚠️ IMPORTANT RULES (DO NOT IGNORE)

Always use 0-based indexing

Always update len

Never break pointer chain

Always check invalid index

📌 4. Add At Head

🖼️ Visualization

💡 Idea

New node becomes the first node.

🪜 Steps

Create new node

Point it to current head

Move head to new node

✅ Code

MyLinkedList . prototype . addAtHead = function ( val ) { const node = new Node ( val );

node . next = this . head ; this . head = node ;

this .…