Linked Lists-Linked Lists: Detect a Cycle.py

#Problem Link : https://www.hackerrank.com/challenges/ctci-linked-list-cycle/problem?isFullScreen=true&h_l=interview&playlist_slugs%5B%5D=interview-preparation-kit&playlist_slugs%5B%5D=linked-lists

#Ans:

"""
Detect a cycle in a linked list. Note that the head pointer may be 'None' if the list is empty.

A Node is defined as: 
 
    class Node(object):
        def __init__(self, data = None, next_node = None):
            self.data = data
            self.next = next_node
"""

def has_cycle(head):
    if (head == None):
        return False
    else:
        slow = head
        fast = head.next
        while (slow != fast) :
            if (fast == None or fast.next == None):
                return False
            else:
                slow = slow.next;
                fast = fast.next.next;
        return True