struct Solution {}
impl Solution {
    fn bit_square(mut n: i32) -> i32 {
        let mut s = 0;
        while n != 0 {
            let i = n % 10;
            s += i * i;
            n /= 10;
        }
        s
    }
    pub fn is_happy(n: i32) -> bool {
        let mut fast = n;
        let mut slow = n;
        loop {
            slow = Self::bit_square(slow);
            fast = Self::bit_square(fast);
            fast = Self::bit_square(fast);
            if slow == fast {
                break;
            }
        }
        slow == 1
    }
}
#[cfg(test)]
mod test {
    use super::*;
    #[test]
    fn test() {
        let t = Solution::is_happy(19);
        assert_eq!(t, true);
    }
}