Method swim

src/common/priority_queue.rs:100–105

(&mut self, mut k: usize)

    }

    fn swim(&mut self, mut k: usize) {
        while k > 1 && self.compare(k / 2, k) {
            self.pq.swap(k, k / 2);
            k /= 2;
        }
    }

    fn sink(&mut self, mut k: usize) {
        let n = self.n;