231. Power of Two
EasyLeetCodeGiven an integer n, return true if it is a power of two. Otherwise, return false.
An integer n is a power of two, if there exists an integer x such that n == 2x.
Example 1:
Input: n = 1
Output: true
Explanation: 20 = 1
Example 2:
Input: n = 16
Output: true
Explanation: 24 = 16
Example 3:
Input: n = 3
Output: false
Constraints:
-231 <= n <= 231 - 1
How to solve the problem
Using while loop.
Using logarithm, if a number is a power of 2, then its log2(n) must be an integer.
Code
- Loop
Python
class Solution:
def isPowerOfTwo(self, n: int) -> bool:
if n <= 0: return False
while n > 1:
if n % 2 != 0: return False
n //= 2
return True
- Logarithm
Python
class Solution:
def isPowerOfTwo(self, n: int) -> bool:
if n <= 0: return False
return math.log2(n).is_integer()
Complexity
Time complexity: O(log n)
The number of iterations is equal to the number of digits in n, which is ⌊log10(n)⌋ + 1.
Space complexity: O(1)
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