Java堆&优先级队列示例讲解(下)

public interface IQueue<E> {
    // 入队
    void offer(E val);
    //出队
    E poll();
    //返回队首元素
    E peek();
    //判断队列是否为空
    boolean isEmpty();
}

/**
 * 基于最大堆的优先级队列,值越大优先级越高
 * 队首元素就是优先级最大的元素(值最大)
 */
 
import stack_queue.queue.IQueue;
 
public class PriorityQueue implements IQueue<Integer> {
    MaxHeap heap = new MaxHeap();
    public PriorityQueue(){
        heap = new MaxHeap();
    }
 
    @Override
    public void offer(Integer val) {
        heap.add(val);
    }
 
    @Override
    public Integer poll() {
        return heap.extractMax();
    }
 
    @Override
    public Integer peek() {
        return heap.peekMax();
    }
 
    @Override
    public boolean isEmpty() {
        return heap.isEmpty();
    }
}

import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.Queue;
 
public class PriorityQueueTest {
    public static void main(String[] args) {
        // 通过构造方法传入比较器
        // 默认是最小堆，"值"(比较器compare的返回值)越小，优先级就越高
        // 当传入一个降序的比较器时,值(比较器compare的返回值，值越大，返回负数)
//        Queue<Student> queue = new PriorityQueue<>(new StudentComDesc());
//        Queue<Student> queue = new PriorityQueue<>(new Comparator<Student>() {
//            @Override
//            public int compare(Student o1, Student o2) {
//                return o2.getAge() - o1.getAge();
//            }
//        });
        Queue<Student> queue = new PriorityQueue<>(new StudentCom());
        Student stu1 = new Student(18,"雷昊");
        Student stu2 = new Student(20,"张超");
        Student stu3 = new Student(16,"钺浦");
        queue.offer(stu1);
        queue.offer(stu2);
        queue.offer(stu3);
        while (!queue.isEmpty()){
            System.out.println(queue.poll());
        }
    }
}
 
//升序（最小堆）
class StudentCom implements Comparator<Student> {
    @Override
    public int compare(Student o1, Student o2) {
        return o1.getAge() - o2.getAge();
    }
}
 
//降序（最大堆）
class StudentComDesc implements Comparator<Student> {
    @Override
    public int compare(Student o1, Student o2) {
        return o2.getAge() - o1.getAge();
    }
}
 
class Student{
    private int age;
    private String name;
 
    public int getAge() {
        return age;
    }
 
    public Student(int age, String name) {
        this.age = age;
        this.name = name;
    }
 
    @Override
    public String toString() {
        return "Student{" +
                "age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}