Given the head of a Singly LinkedList, write a function to determine if the LinkedList has a cycle in it or not.

has_cycle.py

class Node:
  def __init__(self, value, next=None):
    self.value = value
    self.next = next


def has_cycle(head):
  fast_pointer = head
  slow_pointer = head
  while fast_pointer is not None and fast_pointer.next is not None:
    fast_pointer = fast_pointer.next.next
    slow_pointer = slow_pointer.next
    if fast_pointer == slow_pointer:
      return True
  return False


def main():
  head = Node(1)
  head.next = Node(2)
  head.next.next = Node(3)
  head.next.next.next = Node(4)
  head.next.next.next.next = Node(5)
  head.next.next.next.next.next = Node(6)
  print("LinkedList has cycle: " + str(has_cycle(head)))

  head.next.next.next.next.next.next = head.next.next
  print("LinkedList has cycle: " + str(has_cycle(head)))

  head.next.next.next.next.next.next = head.next.next.next
  print("LinkedList has cycle: " + str(has_cycle(head)))


main()