231. Power of Two

题目来源【Leetcode】

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

判断一个数是否为2的N次方

方法一：取对数

class Solution {
public:
    bool isPowerOfTwo(int n) {
        double i = log10(n)/log10(2);
        return (i-(int)i) == 0;
    }
};

方法二：用二进制的特点

class Solution {
public:
    bool isPowerOfTwo(int n) {
      return n > 0 && !(n&(n-1));
    }
};

方法三：用最大的2进制数

class Solution {
public:
    bool isPowerOfTwo(int n) {
      return n > 0 && 4294967296%n == 0;
    }
};