Method dequeue

publication/code/chapter09/find_province_num_bfs.rs:29–35

(&mut self)

    }

    fn dequeue(&mut self) -> Option<T> {
        if self.size() > 0 {
            self.data.pop()
        } else {
            None
        }
    }

    fn is_empty(&self) -> bool {
        0 == self.size()