old_contents: # Time:  O(1)
  # Space: O(1)
  
  # Given an integer (signed 32 bits), write a function to check whether it is a power of 4.
  #
  # Example:
  # Given num = 16, return true. Given num = 5, return false.
  #
  # Follow up: Could you solve it without loops/recursion?
  
  class Solution(object):
      def isPowerOfFour(self, num):
          """
          :type num: int
          :rtype: bool
          """
          return num > 0 and (num & (num - 1)) == 0 and \
                 ((num & 0b1010101010101010101010101010101) == num)
  
  
  # Time:  O(1)
  # Space: O(1)
  class Solution2(object):
      def isPowerOfFour(self, num):
          """
          :type num: int
          :rtype: bool
          """
          while num and not (num & 0b11):
              num >>= 2
          return (num == 1)
  
new_contents: # Time:  O(1)
  # Space: O(1)
  
  # Given an integer (signed 32 bits), write a function to check whether it is a power of 4.
  #
  # Example:
  # Given num = 16, return true. Given num = 5, return false.
  #
  # Follow up: Could you solve it without loops/recursion?
  
  class Solution(object):
      def isPowerOfFour(self, num):
          """
          :type num: int
          :rtype: bool
          """
          return num > 0 and (num & (num - 1)) == 0 and \
                 ((num & 0b01010101010101010101010101010101) == num)
  
  
  # Time:  O(1)
  # Space: O(1)
  class Solution2(object):
      def isPowerOfFour(self, num):
          """
          :type num: int
          :rtype: bool
          """
          while num and not (num & 0b11):
              num >>= 2
          return (num == 1)
  
subject: Update power-of-four.py