342. Power of Four

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Bit

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public boolean isPowerOfFour(int n) {
    if (n <= 0) {
        return false;
    }

    return (n & (n - 1)) == 0 && (n & 0b01010101010101010101010101010101) != 0;
}

Math

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class Solution {
    public boolean isPowerOfFour(int n) {
        if (n <= 0) {
            return false;
        }

        return (n & (n - 1)) == 0 && n % 3 == 1;
    }
}

References

342. Power of Four