find the standard deviation of all nodes in a linked list in ruby

main.rb
# Define the Node class
class Node
  attr_accessor :value, :next_node

  def initialize(value, next_node = nil)
    @value = value
    @next_node = next_node
  end
end

# Define the LinkedList class
class LinkedList
  attr_accessor :head

  def initialize
    @head = nil
  end

  # Method to add a node to the linked list
  def add(number)
    node = Node.new(number)

    if !@head
      @head = node
    else
      current = @head
      while current.next_node != nil
        current = current.next_node
      end
      current.next_node = node
    end
  end

  # Method to calculate the mean of the linked list
  def mean
    sum = 0
    count = 0
    current = @head

    while current != nil
      sum += current.value
      count += 1
      current = current.next_node
    end

    sum.to_f / count
  end

  # Method to calculate the variance of the linked list
  def variance
    sum = 0
    count = 0
    current = @head

    while current != nil
      sum += (current.value - mean) ** 2
      count += 1
      current = current.next_node
    end

    sum.to_f / count
  end

  # Method to calculate the standard deviation of the linked list
  def standard_deviation
    Math.sqrt(variance)
  end
end

# Create a new linked list
list = LinkedList.new
list.add(1)
list.add(2)
list.add(3)
list.add(4)

# Output the standard deviation of the linked list
puts "Standard Deviation: #{list.standard_deviation}"
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