old_contents: # Time:  O(1)
  # Space: O(1)
  
  class Solution(object):
      def bulbSwitch(self, n):
          """
          type n: int
          rtype: int
          """
          return int(math.sqrt(n))
  
new_contents: # Time:  O(1)
  # Space: O(1)
  
  # There are n bulbs that are initially off. 
  # You first turn on all the bulbs. Then, 
  # you turn off every second bulb. On the 
  # third round, you toggle every third bulb 
  # (turning on if it's off or turning off if
  # it's on). For the nth round, you only 
  # toggle the last bulb. Find how many bulbs 
  # are on after n rounds.
  #
  # Example:
  #
  # Given n = 3. 
  #
  # At first, the three bulbs are [off, off, off].
  # After first round, the three bulbs are [on, on, on].
  # After second round, the three bulbs are [on, off, on].
  # After third round, the three bulbs are [on, off, off]. 
  #
  # So you should return 1, because there is 
  # only one bulb is on.
  
  class Solution(object):
      def bulbSwitch(self, n):
          """
          type n: int
          rtype: int
          """
          return int(math.sqrt(n))
  
subject: Update bulb-switcher.py