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package com.base4j.util.lang;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.PriorityQueue;

/**
 * 有界优先队列

 * 按照给定的排序规则，排序元素，当队列满时，按照给定的排序规则淘汰末尾元素（去除末尾元素）
 *
 * @param  成员类型
 * @author xxx
 */
public class BoundedPriorityQueue extends PriorityQueue {
    private static final long serialVersionUID = 3794348988671694820L;

    //容量
    private int capacity;
    private Comparator comparator;

    public BoundedPriorityQueue(int capacity) {
        this(capacity, null);
    }

    /**
     * 构造
     *
     * @param capacity   容量
     * @param comparator 比较器
     */
    public BoundedPriorityQueue(int capacity, final Comparator comparator) {
        super(capacity, new Comparator() {

            @Override
            public int compare(E o1, E o2) {
                int cResult = 0;
                if (comparator != null) {
                    cResult = comparator.compare(o1, o2);
                } else {
                    @SuppressWarnings("unchecked")
                    Comparable o1c = (Comparable) o1;
                    cResult = o1c.compareTo(o2);
                }

                return -cResult;
            }

        });
        this.capacity = capacity;
        this.comparator = comparator;
    }

    /**
     * 加入元素，当队列满时，淘汰末尾元素
     *
     * @param e 元素
     * @return 加入成功与否
     */
    @Override
    public boolean offer(E e) {
        if (size() >= capacity) {
            E head = peek();
            if (this.comparator().compare(e, head) <= 0) {
                return true;
            }
            //当队列满时，就要淘汰顶端队列
            poll();
        }
        return super.offer(e);
    }

    /**
     * 添加多个元素

     * 参数为集合的情况请使用{@link PriorityQueue#addAll}
     *
     * @param c 元素数组
     * @return 是否发生改变
     */
    public boolean addAll(E[] c) {
        return this.addAll(Arrays.asList(c));
    }

    /**
     * @return 返回排序后的列表
     */
    public ArrayList toList() {
        final ArrayList list = new ArrayList(this);
        Collections.sort(list, comparator);

        return list;
    }

    @Override
    public Iterator iterator() {
        return toList().iterator();
    }
}