*Power of Two

题目：

Given an integer, write a function to determine if it is a power of two.

bⁿ is the product of multiplying n bases:

{displaystyle b^{n}=underbrace {b imes cdots imes b} _{n}}

In that case, bⁿ is called the n-th power of b, or b raised to the power n.

解法一：bit

如果是power of two, 则2进制表达中,有且仅有一个1.  可以通过移位来数1的个数, 这里用了一个巧妙的办法, 即判断   N & (N-1) 是否为0. 

public class Solution {
    public boolean isPowerOfTwo(int n) {
       return n > 0 && ((n & (n - 1)) == 0 );
    }
}

解法二：可以应用到power of n

public class Solution {
    public boolean isPowerOfTwo(int n) {
        if(n>1)
        {
            while(n%2==0)
            {
                n=n/2;
            }
        }
        return n==1;
    }
}

reference: http://blog.csdn.net/xudli/article/details/46784163