Delete duplicate nodes from sorted linked list in python

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

#    Python 3 program for
#    Delete duplicate nodes in sorted linked list

#  Linked list node
class LinkNode :
	def __init__(self, data) :
		self.data = data
		self.next = None
	

class SingleLL :
	def __init__(self) :
		self.head = None
		self.tail = None
	
	#  Add new node at the end of linked list
	def addNode(self, value) :
		#  Create a new node
		node = LinkNode(value)
		if (self.head == None) :
			self.head = node
		else :
			self.tail.next = node
		
		self.tail = node
	
	#  Display linked list element
	def display(self) :
		if (self.head == None) :
			return
		
		temp = self.head
		#  iterating linked list elements
		while (temp != None) :
			print(temp.data , end = " → ")
			#  Visit to next node
			temp = temp.next
		
		print(" NULL")
	
	#  Remove the duplicate nodes from sorted singly linked list
	def deleteDuplicate(self) :
		if (self.head == None) :
			return
		else :
			#  Auxiliary variables
			temp = self.head.next
			current = self.head
			hold = None
			#  Find and remove duplicate
			while (temp != None) :
				#  Check duplicate node 
				if (current.data == temp.data) :
					#   When node key are same
					hold = temp
				else :
					#  When node key are not same
					current = temp
				
				#  Visit to next node
				temp = temp.next
				if (hold != None) :
					#  Modified link value
					current.next = temp
					hold = None
				else :
					#  Change last node
					self.tail = current
				
			
		
	

def main() :
	sll = SingleLL()
	#  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")
	sll.display()
	sll.deleteDuplicate()
	print("After Delete")
	#  1 → 2 → 3 → 4 → 5 → 6 → 7 → NULL
	sll.display()

if __name__ == "__main__": 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