342 power of four

首先是power of two, 然后奇数位是1的都不是，比如10, 1000

4 : 1(1), 4(100), 16(10000),

bool isPowerOfFour(int num) {
    
    return num>0 && !(num&0xAAAAAAAA) && !(num&(num-1));
    
}