Use recursion can easy to solve this problem, like below:
class Solution(object):
def isPowerOfFour(self, num):
"""
:type num: int
:rtype: bool
"""
if num == 1: return True
while num > 4:
mod = num % 4
num /= 4
if mod != 0:
return False
return num == 4But we can't use iteration to solve this problem, so the bitwise is the solution and 0X55555555 is special value