kth_to_last_node.rb

  class LinkedListNode

  attr_accessor :value, :next

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

  def kth_to_last_node(k, head)
    # create two pointers at the head node
    trailing_pointer = head
    leading_pointer = head
    # set the leading_pointer k nodes ahead of the trailing_pointer
    k.times do
      leading_pointer = leading_pointer.next
    end
    # advance both leading_ and trailing_pointers. When the leading_pointer reaches the last node, the trailing_pointer will be k nodes from the end.
    until leading_pointer.next == nil
      trailing_pointer = trailing_pointer.next
      leading_pointer = trailing_pointer.next
    end
    puts "The value of the Kth node from the end of the linked list is #{trailing_pointer.value}"
  end
end

a = LinkedListNode.new("Angel Food")
b = LinkedListNode.new("Bundt")
c = LinkedListNode.new("Cheese")
d = LinkedListNode.new("Devil's Food")
e = LinkedListNode.new("Eccles")

a.next = b
b.next = c
c.next = d
d.next = e

a.kth_to_last_node(2, a)
# returns the node with value "Devil's Food" (the 2nd to last node)