A Common-Sense Guide to Data Structures and Algorithms by Jay Wengrow. Linked List Insertion method


A Common-Sense Guide to Data Structures and Algorithms - insertion at wrong index (page 140)

I tested the example of a linked list insertion method on page 140 (2017 edition):

class Node
  attr_accessor :data, :next_node
  def initialize(data) 
    @data = data

class LinkedList
  attr_accessor :first_node
  # rest of code omitted here...

  def insert_at_index(index, value) 
    current_node = first_node 
    current_index = 0

    # First, we find the index immediately before where the new node will go:
     while current_index < index do
       current_node = current_node.next_node
       current_index += 1

     # We create the new node:
     new_node = Node.new(value)
     new_node.next_node = current_node.next_node
     # We modify the link of the previous node to point to our new node:
     current_node.next_node = new_node

The method seems to be inserting a new node after the provided index, e.g.

node_1 = Node.new("once") 
node_2 = Node.new("upon") 
node_1.next_node = node_2
node_3 = Node.new("a") 
node_2.next_node = node_3
node_4 = Node.new("time") 
node_3.next_node = node_4

list = LinkedList.new(node_1)  # 0. "once" 1. "upon" 2. "a" 3. "time"
list.insert_at_index(3, "beautiful") # 0 "once" 1. "upon" 2. "a" 3. "time" 4. "beautiful"

Shouldn’t the while loop be while current_index < index-1 instead?

Thank you for the brilliant book anyway @jaywengrow . It’s a great learning resource!

Thanks for this! You are correct, and this has indeed been fixed in the Second Edition of the book.