Linked list cycle detection. Python solution for https://www.hackerrank.com/challenges/detect-whether-a-linked-list-contains-a-cycle

cycle_detectipn.py

"""
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
    
    tortoise = hare = head
    
    while(tortoise or hare or hare.next):
        
        if hare.next == None:
            return False
        
        if tortoise == hare.next:
            return True
        
        tortoise = tortoise.next
        hare = hare.next.next
        
    return False