5：大顶堆： 最大优先队列

1:  与前面说的最小优先队列相反

 

 堆的排序也相反 ： 

 

package com.algorithm.common;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * 大顶堆排序 最大优先队列
 * @author lijunqing
 */
public class MaxPQ<Key> implements Iterable<Key> {

    private int N;

    private Key[] pq;

    public MaxPQ() {
        this(1);
        N=0;
    }

    public MaxPQ(int initCapacity) {
        pq=(Key[])new Object[initCapacity + 1];
        N=0;
    }

    /**
     * 添加一个到堆中
     * @param key
     */
    public void insert(Key key) {
        if(N == pq.length - 1) { // 申请2培空间
            resize(2 * pq.length);
        }
        N++;
        pq[N]=key;
        swim(N);
    }

    /**
     * 递归调整当前节点和父节点的
     * @param n2
     */
    private void swim(int i) {
        while(i > 1 && greater(i, i / 2)) {
            exch(i, i / 2);
            i=i / 2;
        }
    }

    /**
     * 堆顶出堆 重新调整堆
     * @return
     */
    public Key delMax() {
        exch(1, N);
        Key max=pq[N];
        pq[N]=null;
        N--;
        skin(1);
        return max;
    }

    /**
     * 从i节点开始调整堆
     * @param i
     */
    private void skin(int i) {
        while(2 * i <= N) {
            int k=2 * i;
            if(k < N && greater(k+1, k)) {
                k++;
            }
            if(greater(i, k)){
                break;
            }
            exch(i, k);
            i=k;
        }
    }

    /**
     * i节点大于j节点
     * @param i
     * @param i2
     * @return
     */
    private boolean greater(int i, int j) {
        return ((Comparable<Key>)pq[i]).compareTo(pq[j]) > 0;
    }

    /**
     * 重新申请空间
     * @param capacity
     */
    private void resize(int capacity) {
        Key[] temp=(Key[])new Object[capacity];
        for(int i=0; i < pq.length; i++) {
            temp[i]=pq[i];
        }
        pq=temp;
    }

    /**
     * 交互节点值
     * @param i
     * @param j
     */
    private void exch(int i, int j) {
        Key temp=pq[i];
        pq[i]=pq[j];
        pq[j]=temp;
    }

    public int size() {
        return N;
    }

    public boolean isEmpty() {
        return N == 0;
    }

    @Override
    public Iterator<Key> iterator() {
        return new HeapIterator();
    }

    private class HeapIterator implements Iterator<Key> {

        // 重新建一个
        private MaxPQ<Key> copy;

        public HeapIterator() {
            copy=new MaxPQ<Key>(size());
            for(int i=1; i <= N; i++)
                copy.insert(pq[i]);
        }

        public boolean hasNext() {
            return !copy.isEmpty();
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }

        public Key next() {
            if(!hasNext())
                throw new NoSuchElementException();
            return copy.delMax();
        }
    }

    public static void main(String[] agrs) {
        MaxPQ<Integer> max=new MaxPQ<Integer>();
        max.insert(22);
        max.insert(1);
        max.insert(56);
        max.insert(41);
        max.insert(3);
        max.insert(27);
        Iterator<Integer> m = max.iterator();
        while(m.hasNext()){
            System.out.println(m.next());
        }
    }

}

 

结果：

56
41
27
22
3
1