Class PQ

src/common/priority_queue.rs:15–19

type Comparator<T> = Box<dyn Fn(&T, &T) -> bool>;

pub struct PQ<T> {
    pq: Vec<T>, // 为了计算方便, pq的index是从1开始计算的, 0号元素未被使用
    n: usize,
    comparator: Comparator<T>,
}

pub struct IndexPQ<T> {
    // max_n: usize, // maximum number of elements on PQ