O(1)检测2的幂次

class Solution {
public:
    /*
     * @param n: An integer
     * @return: True or false
     */
    bool checkPowerOf2(int n) {
        // write your code here
        if(n <= 0)
            return false;
        int sum = 0;
        while(n){
            sum += (n&1);
            n >>= 1;
        }
        if(sum == 1)
            return true;
        return false;
    }
};