package org.loda.structure;

/**

*

* @ClassName: MinQ

* @Description: 从小到大排列的优先队列

* @author minjun

* @date 2015年5月20日 上午10:01:29

*

*/

@SuppressWarnings("unchecked")

public class MinQ> {

// 利用数组存储队列元素

private Item[] items;

// 队列元素数量

private int heapSize;

// 初始化队列大小

private int size = 0;

public MinQ() {

this(10);

}

public MinQ(int size) {

this.size = size;

items = (Item[]) new Comparable[size];

}

// 添加元素

public void offer(Item item) {

if (heapSize == size)

resize();

items[heapSize++] = item;

shiftUp(heapSize - 1);

}

//两倍扩容数组

private void resize() {

this.size=this.size<<1;

Item[] newItems=(Item[]) new Comparable[size];

for(int i=0;i

newItems[i]=items[i];

}

items=newItems;

}

// 获取优先级最高的元素

public Item poll() {

if (isEmpty())

throw new RuntimeException("没有元素了");

Item item = items[0];

items[0] = null;

exchange(0, --heapSize);

shiftDown(0);

return item;

}

// 判断队列是否为空

public boolean isEmpty() {

return heapSize == 0;

}

//获取队列中元素的个数

public int size(){

return heapSize;

}

//打印优先队列中的堆结构

public void print() {

System.out.println("===================");

for (int i = 0; i < heapSize && left(i) < heapSize

&& right(i) < heapSize; i++) {

System.out.print(items[i] + "\t左：" + items[left(i)] + ",右："

+ items[right(i)] + "\t");

System.out.println();

}

System.out.println("===================");

}

// 上移

private void shiftUp(int i) {

int parent = parent(i);

if (i > 0 && less(items[i], items[parent])) {

exchange(i, parent);

shiftUp(parent);

}

}

// 下沉

private void shiftDown(int i) {

int left = left(i);

int right = right(i);

int least = i;

if (left < heapSize && less(items[left], items[i])) {

least = left;

}

if (right < heapSize && less(items[right], items[least])) {

least = right;

}

if (least != i) {

exchange(least, i);

shiftDown(least);

}

}

// a是否小于b

private boolean less(Item a, Item b) {

return a.compareTo(b) < 0;

}

// 右孩子节点

private int right(int i) {

return i * 2 + 2;

}

// 左孩子节点

private int left(int i) {

return i * 2 + 1;

}

// 父节点

private int parent(int i) {

return (i - 1) / 2;

}

private void exchange(int i, int j) {

Item t = items[i];

items[i] = items[j];

items[j] = t;

}

public static void main(String[] args) {

//MinQ q = new MinQ();

//

//for (int i = 0; i < 10; i++) {

//q.offer(Math.round((float) Math.random() * 100));

//}

MinQ q = new MinQ();

q.offer("jack");

q.offer("shelock");

q.offer("allen");

q.offer("andy");

q.offer("jetty");

q.print();

while (!q.isEmpty()) {

System.out.println(q.poll());

}

}

}