231-Power of Two

100-Same Tree | Links:

题意

Given 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 == 2^x.

Example 1:
Input: n = 1
Output: true
Explanation: 2^0 = 1

Example 2:
Input: n = 16
Output: true
Explanation: 2^4 = 16

Example 3:
Input: n = 3
Output: false

Example 4:
Input: n = 4
Output: true

Example 5:
Input: n = 5
Output: false

思路

• 位运算：n&(n-1) ==0 判断2的整数次幂

class Solution(object):
    def isPowerOfTwo(self, n):
        """
        :type n: int
        :rtype: bool
        """
        if n <= 0: return False
        return n & (n-1)==0

分析:

• Time: O(1)
• Space: O(1)