Rotate a linked list by k nodes in ruby

Ruby program for Rotate a linked list by k nodes. Here problem description and other solutions.

#  Ruby program for
#  Rotate a linked list

#  Linked list node
class LinkNode 
	# Define the accessor and reader of class LinkNode
	attr_reader :data, :next
	attr_accessor :data, :next
	def initialize(data) 
		self.data = data
		self.next = nil
	end
end

class SingleLL 
	# Define the accessor and reader of class SingleLL
	attr_reader :head, :tail
	attr_accessor :head, :tail
	def initialize() 
		self.head = nil
		self.tail = nil
	end

	#  Add new node at the end of linked list
	def insert(value) 
		#  Create a new node
		node = LinkNode.new(value)
		if (self.head == nil) 
			self.head = node
		else
			self.tail.next = node
		end
		self.tail = node
	end

	#  Display linked list element
	def display() 
		if (self.head == nil) 
			return
		end

		temp = self.head
		#  iterating linked list elements
		while (temp != nil) 
			print(temp.data ," → ")
			#  Visit to next node
			temp = temp.next
		end

		print("NULL\n")
	end

	def validKNode(k) 
		temp = self.head
		count = 0
		#  Count node
		while (temp != nil) 
			count += 1
			if (count > k) 
				#  When K is correct
				return k
			end

			#  Visit to next node
			temp = temp.next
		end

		#  Need to change k value
		return k % count
	end

	def rotate(k) 
		if (k <= 0) 
			return
		end

		if (self.head == nil) 
			print("Empty linked list\n")
			return
		end

		#  Assume that k is less the number of nodes
		#  Otherwise first count number of nodes 
		#  Then use modulo operator and change k = k % count
		#  Here implement
		k = self.validKNode(k)
		if (k == 0) 
			#  because after rotate get same result
			return
		else
 
			#  Use to find the location of rotate node
			counter = 1
			point = nil
			temp = self.head
			#  Find last node in rotation
			while (temp != nil && temp.next != nil) 
				if (counter == k) 
					point = temp
				end

				counter += 1
				temp = temp.next
			end

			#  When roated node are exist
			if (point != nil) 
				#  Modified node position
				temp.next = self.head
				#  Modified head
				self.head = point.next
				#  Modified tail
				self.tail = point
				point.next = nil
			end

		end

	end

end

def main() 
	sll = SingleLL.new()
	k = 3
	#  Linked list
	#  1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL
	sll.insert(1)
	sll.insert(2)
	sll.insert(3)
	sll.insert(4)
	sll.insert(5)
	sll.insert(6)
	sll.insert(7)
	sll.insert(8)
	print("Before Rotate ", k ," Nodes\n")
	sll.display()
	#  Rotate node
	sll.rotate(k)
	print("After Rotate ", k ," Nodes\n")
	sll.display()
end

main()

Output

Before Rotate 3 Nodes
1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL
After Rotate 3 Nodes
4 → 5 → 6 → 7 → 8 → 1 → 2 → 3 → NULL