Rotate a linked list by k nodes in python

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

#  Python 3 program for
#  Rotate a 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 insert(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")
	
	def validKNode(self, k) :
		temp = self.head
		count = 0
		#  Count node
		while (temp != None) :
			count += 1
			if (count > k) :
				#  When K is correct
				return k
			
			#  Visit to next node
			temp = temp.next
		
		#  Need to change k value
		return k % count
	
	def rotate(self, k) :
		if (k <= 0) :
			return
		
		if (self.head == None) :
			print("Empty linked list")
			return
		
		#  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 = None
			temp = self.head
			#  Find last node in rotation
			while (temp != None and temp.next != None) :
				if (counter == k) :
					point = temp
				
				counter += 1
				temp = temp.next
			
			#  When roated node are exist
			if (point != None) :
				#  Modified node position
				temp.next = self.head
				#  Modified head
				self.head = point.next
				#  Modified tail
				self.tail = point
				point.next = None
			
		
	

def main() :
	sll = SingleLL()
	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")
	sll.display()
	#  Rotate node
	sll.rotate(k)
	print("After Rotate ", k ," Nodes")
	sll.display()

if __name__ == "__main__": 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