https://leetcode.com/problems/power-of-two/

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

数字 2^n 是大于0的，而且等于1左移n位得到的数字，所以2^n与2^n-1 相与运算得到0.

bool isPowerOfTwo(int n) {if(n <= 0)return false;if((n & (n-1)) == 0)return true;return false;
}

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