HTMLify

# Definition for singly-linked list.
# class ListNode
#     attr_accessor :val, :next
#     def initialize(val)
#         @val = val
#         @next = nil
#     end
# end

# @param {ListNode} head
# @return {Boolean}
def hasCycle(head)
  p1 = p2 = head
  while p1 and p2 and p2.next
    p1 = p1.next
    p2 = p2.next.next
    if p1 == p2 then
      return true
    end
  end
  return false
end