power_of_four.rs

// Time:  O(1)
// Space: O(1)
pub struct Solution1 {}
impl Solution1 {
    pub fn is_power_of_four(num: i32) -> bool {
        num > 0 && (num & (num - 1)) == 0 && ((num & 0b01010101010101010101010101010101) == num)
    }
}

// Time:  O(1)
// Space: O(1)
pub struct Solution2 {}
impl Solution2 {
    pub fn is_power_of_four(mut num: i32) -> bool {
        while num != 0 && (num & 0b11) == 0 {
            num >>= 2;
        }
        num == 1
    }
}

// https://github.com/kamyu104/LeetCode-Solutions/blob/master/Python/power-of-four.py#L27-L34
// pub struct Solution3 {}
// impl Solution3 {
//     pub fn is_power_of_four(num: i32) -> bool {
//     }
// }

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_is_power_of_four() {
        assert_eq!(Solution1::is_power_of_four(16), true);
        assert_eq!(Solution1::is_power_of_four(5), false);

        assert_eq!(Solution2::is_power_of_four(16), true);
        assert_eq!(Solution2::is_power_of_four(5), false);

        // assert_eq!(Solution3::is_power_of_four(16), true);
        // assert_eq!(Solution3::is_power_of_four(5), false);
    }
}