How to Implement Linked List in Ruby: Simple Guide

To implement a linked list in Ruby, create a Node class to hold data and a reference to the next node, then build a LinkedList class to manage nodes. Use methods to add, remove, and traverse nodes, linking each node to the next.

Syntax

A linked list in Ruby typically uses two classes: Node and LinkedList.

• Node holds the value and a reference to the next node.
• LinkedList manages the list by keeping track of the head node and providing methods to add or remove nodes.

ruby

class Node
  attr_accessor :value, :next

  def initialize(value)
    @value = value
    @next = nil
  end
end

class LinkedList
  attr_accessor :head

  def initialize
    @head = nil
  end

  def append(value)
    new_node = Node.new(value)
    if @head.nil?
      @head = new_node
    else
      current = @head
      current = current.next while current.next
      current.next = new_node
    end
  end

  def display
    current = @head
    while current
      print "#{current.value} -> "
      current = current.next
    end
    puts "nil"
  end
end

Example

This example shows how to create a linked list, add nodes, and display the list.

ruby

class Node
  attr_accessor :value, :next

  def initialize(value)
    @value = value
    @next = nil
  end
end

class LinkedList
  attr_accessor :head

  def initialize
    @head = nil
  end

  def append(value)
    new_node = Node.new(value)
    if @head.nil?
      @head = new_node
    else
      current = @head
      current = current.next while current.next
      current.next = new_node
    end
  end

  def display
    current = @head
    while current
      print "#{current.value} -> "
      current = current.next
    end
    puts "nil"
  end
end

list = LinkedList.new
list.append(10)
list.append(20)
list.append(30)
list.display

Output

10 -> 20 -> 30 -> nil

Common Pitfalls

Common mistakes when implementing linked lists in Ruby include:

• Not updating the next pointer correctly, causing broken links.
• Forgetting to handle the case when the list is empty (head is nil).
• Not traversing the list properly, which can cause infinite loops or missed nodes.

Always check if head is nil before traversing, and update next pointers carefully.

ruby

class LinkedList
  attr_accessor :head

  def initialize
    @head = nil
  end

  # Wrong: Does not handle empty list
  def append_wrong(value)
    return @head = Node.new(value) if @head.nil?
    current = @head
    current = current.next while current.next
    current.next = Node.new(value)
  end

  # Right: Handles empty list
  def append_right(value)
    new_node = Node.new(value)
    if @head.nil?
      @head = new_node
    else
      current = @head
      current = current.next while current.next
      current.next = new_node
    end
  end
end

Quick Reference

• Node: Holds data and pointer to next node.
• LinkedList: Manages nodes, tracks head.
• append(value): Adds new node at end.
• display: Prints all node values.
• Always check for empty list before operations.

Key Takeaways

A linked list uses nodes that hold data and a reference to the next node.

Always handle the empty list case when adding or traversing nodes.

Traverse nodes carefully to avoid infinite loops or missing elements.

Use clear methods like append and display to manage the list.

Test your linked list with simple examples to ensure correctness.