Delete duplicate nodes from sorted linked list in ruby

Ruby program for Delete duplicate nodes from sorted linked list. Here problem description and explanation.

#    Ruby program for
#    Delete duplicate nodes in sorted 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 addNode(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

	#  Remove the duplicate nodes from sorted singly linked list
	def deleteDuplicate() 
		if (self.head == nil) 
			return
		else
 
			#  Auxiliary variables
			temp = self.head.next
			current = self.head
			hold = nil
			#  Find and remove duplicate
			while (temp != nil) 
				#  Check duplicate node 
				if (current.data == temp.data) 
					#   When node key are same
					hold = temp
				else
 
					#  When node key are not same
					current = temp
				end

				#  Visit to next node
				temp = temp.next
				if (hold != nil) 
					#  Modified link value
					current.next = temp
					hold = nil
				else
 
					#  Change last node
					self.tail = current
				end

			end

		end

	end

end

def main() 
	sll = SingleLL.new()
	#  Sorted Linked list node
	#   1 → 1 → 2 → 3 → 4 → 4 → 4 → 5 → 6 → 7 → NULL
	sll.addNode(1)
	sll.addNode(1)
	sll.addNode(2)
	sll.addNode(3)
	sll.addNode(4)
	sll.addNode(4)
	sll.addNode(4)
	sll.addNode(5)
	sll.addNode(6)
	sll.addNode(7)
	print(" Before Delete\n")
	sll.display()
	sll.deleteDuplicate()
	print(" After Delete\n")
	#  1 → 2 → 3 → 4 → 5 → 6 → 7 → NULL
	sll.display()
end

main()

Output

 Before Delete
1 → 1 → 2 → 3 → 4 → 4 → 4 → 5 → 6 → 7 →  NULL
 After Delete
1 → 2 → 3 → 4 → 5 → 6 → 7 →  NULL