struct Drops {
    num: u32,
    drops: Option<String>
}

impl Drops {
    pub fn new(num: u32) -> Drops {
        Drops { num, drops: None }
    }

    pub fn add_if_factor(&mut self, div: u32, suffix: &str) {
        if self.num % div == 0 {
            self.drops.get_or_insert(String::new()).push_str(suffix);
        }
    }

    pub fn get(self) -> String {
        self.drops.unwrap_or(self.num.to_string())
    }
}

pub fn raindrops(n: u32) -> String {
    let mut drops = Drops::new(n);
    drops.add_if_factor(3, "Pling");
    drops.add_if_factor(5, "Plang");
    drops.add_if_factor(7, "Plong");
    drops.get()
}