Can you explain what a linked list is and how it is structured?

A linked list is a data structure consisting of nodes, where each node contains data and a reference to the next node in the list. Unlike arrays, linked lists do not require a contiguous block of memory and allow efficient insertion and deletion of elements.

Main types of linked lists:

• Singly linked list: each node contains a reference only to the next node.
• Doubly linked list: each node contains references to both the next and previous nodes.

Example of a singly linked list in JavaScript (Node.js):

class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
  }
}

class LinkedList {
  constructor() {
    this.head = null;
  }

  add(value) {
    const newNode = new Node(value);
    if (!this.head) {
      this.head = newNode;
    } else {
      let current = this.head;
      while (current.next) {
        current = current.next;
      }
      current.next = newNode;
    }
  }
}

Linked lists are useful when dynamic resizing of the structure and frequent insertions/deletions are required.