Description
Given an integer n, return true if it is a power of four. Otherwise, return false.
An integer n is a power of four, if there exists an integer x such that n == 4x.
Example 1:
Input: n = 16 Output: true
Example 2:
Input: n = 5 Output: false
Example 3:
Input: n = 1 Output: true
Constraints:
-231 <= n <= 231 - 1
Follow up: Could you solve it without loops/recursion?
Solution
Python3
class Solution:
def isPowerOfFour(self, n: int) -> bool:
# 1. there is only one set bit
# 2. the set bit must be at odd position (from left)
if n < 0: return False
for k in range(0, 32, 2):
if (1 << k) == n: return True
return False