利用优先级队列找出十万数据中的最小十个(Find the smallest ten datas in one hundred thousand by priorityQueue)

利用优先级队列,找出十万数据中最小的十个

Find the smallest ten datas in one hundred thousand by priorityQueue

方法:优先级队列,传入的比较器 用大根堆模式来实现.
队列里面只存储十个数据,然后依次遍历十万个数据.
如果遍历的数据比队列顶部的最大值还大,则不管它.
如果遍历的数据比队列顶部的最大值还小,队列中remove掉顶部元素,再将该元素插入进去
Process:1.Creat a priorityQueue with initalCapacity ten and a Comparator that realize big root heap.
        2.Put ten datas into priorityQueue,
        3.Go through the left datas in Arraylist, if the data big than heapTop,pass it
        else remove the top data that in the priorityQueue and put currentData into priorityQueue.
        4.finally,System out the datas in the priority, that's the smallest ten datas;

 public class TestComp {
    public static void main(String[] args) {
        final int NUM = 100000; //规定十万给数据
        int i = 0; //做判断用
        Random random = new Random(  );
        ArrayList<Integer> arrayList = new ArrayList<Integer>(NUM); //存储十万个数据
        while (i < NUM){
            arrayList.add( random.nextInt(NUM));
            i++;
        }

        PriorityQueue<Integer> integerPriorityQueue =
                new PriorityQueue<>( 10, new Comparator<Integer>() {
                    @Override
                    public int compare(Integer o1, Integer o2) {
                        return o2.compareTo( o1 );
                    }
                } );    //创建一个优先级队列,创建一个新的Comparator比较器.实现从大到小排序.

        /**
         * 先把前十个添加进去
         */
        Iterator<Integer> iterator = arrayList.iterator();
        for (int j = 0; j < 10 ; j++) {
            integerPriorityQueue.add( iterator.next() );
        }

       //再继续遍历剩余数据
        while (iterator.hasNext()){
            Integer integer = iterator.next(); //当前遍历的数据
            Integer integer2 = integerPriorityQueue.peek();  //当前优先级队列的堆顶数据.
            if(integer2 > integer){
                integerPriorityQueue.remove(integer2);
                integerPriorityQueue.add( integer );
            }
        }

        //打印最终的十个数据
        Iterator<Integer> iterator2 = integerPriorityQueue.iterator();
        while (iterator2.hasNext()){
            System.out.println(iterator2.next());
        }
    }
}