HTMLify

def remove_nth_from_end(head, n)
  if not head or not head.next then
    return nil
  end

  len = 0
  th = head
  while th do
    th = th.next
    len+=1
  end

  target = len - n
  if target == 0 then
    return head.next
  end
  th = head
  prev = th
  while target > 0 and th do
    prev = th
    th = th.next
    target -= 1
  end

  prev.next = th.next

  return head
end