LeetCode 231: Problem in finding whether a given number is Power of 2

I want to find whether a given number is a power of two in a mathematical way, not with a bitwise approach. Here is my code:

private static double logBaseTwo(final double x) {
    return Math.log(x) / Math.log(2);
}

private static double roundToNearestHundredThousandth(final double x) {
    return Math.round(x * 100000.0) / 100000.0;
}

private static boolean isInteger(final double x) {
    return (int)(Math.ceil(x)) == (int)(Math.floor(x));
}

public static boolean isPowerOfTwo(final int n) {
    return isInteger(roundToNearestHundredThousandth(logBaseTwo(n)));
}

It incorrectly returns true for certain numbers, such as 524287. Why is that?

Your code fails because you may need more precision than you allow to capture the difference between the logs of BIG_NUMBER and BIG_NUMBER+1

The bitwise way is really best, but if you really want to use only "mathy" operations, then the best you can do is probably:

public static boolean isPowerOfTwo(final int n) {
   int exp = (int)Math.round(logBaseTwo(n));
   int test = (int)Math.round(Math.pow(2.0,exp));
   return test == n;
}

This solution does not require any super-fine precision, and will work fine for all positive ints.