Python Program For Finding The Length Of Loop In Linked List

# Python program to detect a loop and 
# find the length of the loop
# Node defining class
class Node:
    
    # Function to make a node
    def __init__(self, val):
        self.val = val
        self.next = None
    
# Linked List defining and loop 
# length finding class 
class LinkedList:
    
    # Function to initialize the 
    # head of the linked list
    def __init__(self):
        self.head = None        
        
    # Function to insert a new 
    # node at the end 
    def AddNode(self, val):
        if self.head is None:
            self.head = Node(val)
        else:
            curr = self.head
            while(curr.next):
                curr = curr.next
            curr.next = Node(val)
    
    # Function to create a loop in the 
    # Linked List. This function creates 
    # a loop by connecting the last node 
    # to n^th node of the linked list, 
    # (counting first node as 1)
    def CreateLoop(self, n):
        
        # LoopNode is the connecting node to
        # the last node of linked list
        LoopNode = self.head
        for _ in range(1, n):
            LoopNode = LoopNode.next
            
        # end is the last node of the 
        # Linked List
        end = self.head
        while(end.next):
            end = end.next
            
        # Creating the loop
        end.next = LoopNode
        
    # Function to detect the loop and return
    # the length of the loop if the returned 
    # value is zero, which means that either 
    # the linked list is empty or the linked 
    # list doesn't have any loop
    def detectLoop(self):
        
        # If linked list is empty then there 
        # is no loop, so return 0
        if self.head is None:
            return 0
        
        # Using Floyd’s Cycle-Finding 
        # Algorithm/ Slow-Fast Pointer Method
        slow = self.head
        fast = self.head

        # To show that both slow and fast 
        # are at start of the Linked List
        flag = 0 
                 
        while(slow and slow.next and fast and
              fast.next and fast.next.next):
            if slow == fast and flag != 0:
                
                # Means loop is confirmed in the 
                # Linked List. Now slow and fast 
                # are both at the same node which
                # is part of the loop
                count = 1
                slow = slow.next
                while(slow != fast):
                    slow = slow.next
                    count += 1
                return count
            
            slow = slow.next
            fast = fast.next.next
            flag = 1
        return 0 # No loop
    
# Setting up the code
# Making a Linked List and 
# adding the nodes
myLL = LinkedList()
myLL.AddNode(1)
myLL.AddNode(2)
myLL.AddNode(3)
myLL.AddNode(4)
myLL.AddNode(5)

# Creating a loop in the linked List
# Loop is created by connecting the 
# last node of linked list to n^th node
# 1<= n <= len(LinkedList)
myLL.CreateLoop(2)

# Checking for Loop in the Linked List 
# and printing the length of the loop
loopLength = myLL.detectLoop()
if myLL.head is None:
    print("Linked list is empty")
else:
    print(str(loopLength))
# This code is contributed by _Ashutosh