O(1) Check Power of 2详解编程语言

Using O(1) time to check whether an integer n is a power of 2. 
 
Example 
For n=4, return true; 
 
For n=5, return false; 
 
Challenge 
O(1) time

0100 ==> 4 
0011 ==> 3

class Solution { 
public: 
    /* 
     * @param n: An integer 
     * @return: True or false 
     */ 
    bool checkPowerOf2(int n) { 
        if (1 > n) { 
            return false; 
        } else { 
            return 0 == (n & (n - 1)); 
        } 
    } 
};

class Solution { 
    /* 
     * @param n: An integer 
     * @return: True or false 
     */ 
    public boolean checkPowerOf2(int n) { 
        if (n < 1) { 
            return false; 
        } else { 
            return (n & (n - 1)) == 0; 
        } 
    } 
};