```
bool isPowerOfFour(int num) {
return num > 0 && (num&(num-1))==0 && (num&(0xAAAAAAAA))==0;
}
(num & (num-1)) == 0 mean num is power of two
(num & (0xAAAAAAAA)) == 0 mean num in binary do not have even bit 1, something like 1010
combine those, the num is power of four.
```