class Node:

def __init__(self,data):

self.data=data

self.next=None

class LinkedList:

def __init__(self):

self.head=None

def insertBeg(self,key):

newNode=Node(key)

newNode.next=self.head

self.head=newNode

def detectLoop(self):

s=[]

temp=self.head

while(temp):

if temp in s:

return True

else:

s.append(temp)

temp=temp.next

return False

llist=LinkedList()

llist.insertBeg(20)

llist.insertBeg(4)

llist.insertBeg(15)

llist.insertBeg(10)

#llist.head.next = llist.head

if( llist.detectLoop()):

print ("Loop found")

else :

print ("No Loop ")

#using Floyd's cycle-Finding algorithm

class LinkedList2:

def __init__(self):

self.head=None

def insertBeg(self,key):

newNode=Node(key)

newNode.next=self.head

self.head=newNode

def detectLoop(self):

slow_p=self.head

fast_p=self.head

while(slow_p and fast_p and fast_p.next):

slow_p=slow_p.next

fast_p=fast_p.next.next

if slow_p==fast_p:

print("Loop Found")

return

print("Loop not found")

llist=LinkedList2()

llist.insertBeg(20)

llist.insertBeg(4)

llist.insertBeg(15)

llist.insertBeg(10)

llist.detectLoop()