342. Power of Four

QUESTION:

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example: Given num = 16, return true. Given num = 5, return false.

Follow up: Could you solve it without loops/recursion?

Credits: Special thanks to @yukuairoy for adding this problem and creating all test cases.

EXPLANATION:

就是只要余数不是0的时候，就一直除以4，到最后就可以了。

SOLUTION:

public boolean isPowerOfFour(int num) {
        if(num == 0) return false;
        while(num>0 && num % 4 == 0){
            num = num>>2;
        }
        return num == 1;
    }
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