Method back

1472-design-browser-history.rs:21–30

(&mut self, steps: i32)

    }

    fn back(&mut self, steps: i32) -> String {
        let steps = steps as usize;
        if self.idx < steps {
            self.idx = 0;
        } else {
            self.idx -= steps;
        }
        // println!("{:?} {:?}", self.his, self.idx);
        self.his[self.idx].clone()
    }

    fn forward(&mut self, steps: i32) -> String {
        let steps = steps as usize;