142. O(1) Check Power of 2【easy】

142. O(1) Check Power of 2【easy】

Using O(1) time to check whether an integer n is a power of 2.

Have you met this question in a real interview? 

Yes

Example

For n=4, return true;

For n=5, return false;

Challenge 

O(1) time

 

解法一：

 1 class Solution {
 2 public:
 3     /*
 4      * @param n: An integer
 5      * @return: True or false
 6      */
 7     bool checkPowerOf2(int n) {
 8         if (n > 0 && (n & n - 1) == 0) {
 9             return true;
10         }
11         
12         return false;
13     }
14 };