Oct 15, 2020
diff --git a/Loop linked list b/Loop linked list
 # Python program to detect loop
 # in the linked list

 # Node class
 class Node:

    # Constructor to initialize
    # the node object
    def __init__(self, data):
        self.data = data
        self.next = None

 class LinkedList:

    # Function to initialize head
    def __init__(self):
        self.head = None

    # Function to insert a new
    # node at the beginning
    def push(self, new_data):
        new_node = Node(new_data)
        new_node.next = self.head
        self.head = new_node

    # Utility function to print it
    # the linked LinkedList
    def printList(self):
        temp = self.head
        while(temp):
            print (temp.data, end =" ")
            temp = temp.next


    def detectLoop(self):
         s = set()
         temp = self.head
         while (temp):

             # If we have already has
             # this node in hashmap it
             # means their is a cycle
             # (Because you we encountering
             # the node second time).
            if (temp in s):
                return True

            # If we are seeing the node for
            # the first time, insert it in hash
            s.add(temp)

            temp = temp.next


         return False

 # Driver program for testing
 llist = LinkedList()
 llist.push(20)
 llist.push(4)
 llist.push(15)
 llist.push(10)

 # Create a loop for testing
 llist.head.next.next.next.next = llist.head;

 if( llist.detectLoop()):
    print ("Loop found")
 else :
    print ("No Loop ")
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,72 @@
		# Python program to detect loop
		# in the linked list

		# Node class
		class Node:

		# Constructor to initialize
		# the node object
		def __init__(self, data):
		self.data = data
		self.next = None

		class LinkedList:

		# Function to initialize head
		def __init__(self):
		self.head = None

		# Function to insert a new
		# node at the beginning
		def push(self, new_data):
		new_node = Node(new_data)
		new_node.next = self.head
		self.head = new_node

		# Utility function to print it
		# the linked LinkedList
		def printList(self):
		temp = self.head
		while(temp):
		print (temp.data, end =" ")
		temp = temp.next


		def detectLoop(self):
		s = set()
		temp = self.head
		while (temp):

		# If we have already has
		# this node in hashmap it
		# means their is a cycle
		# (Because you we encountering
		# the node second time).
		if (temp in s):
		return True

		# If we are seeing the node for
		# the first time, insert it in hash
		s.add(temp)

		temp = temp.next


		return False

		# Driver program for testing
		llist = LinkedList()
		llist.push(20)
		llist.push(4)
		llist.push(15)
		llist.push(10)

		# Create a loop for testing
		llist.head.next.next.next.next = llist.head;

		if( llist.detectLoop()):
		print ("Loop found")
		else :
		print ("No Loop ")