fn main() {
    println!("Hello, world!");
}

fn try_reverse(x: i32) -> Option<i32> {
    let mut i = x;
    let mut result: i32 = 0;

    while i != 0 {
        let digit = i % 10;
        result = result.checked_mul(10)?.checked_add(digit)?;

        i /= 10;
    }

    Some(result)
}

pub fn reverse(x: i32) -> i32 {
    try_reverse(x).unwrap_or(0)
}

#[cfg(test)]
mod tests {
    use crate::reverse;

    #[test]
    fn test_1() {
        assert_eq!(reverse(123), 321);
    }
    #[test]
    fn test_2() {
        assert_eq!(reverse(-123), -321);
    }
    #[test]
    fn test_3() {
        assert_eq!(reverse(120), 21);
    }
    #[test]
    fn test_4() {
        assert_eq!(reverse(1534236469), 0);
    }
}