取k个最小数

PriorityQueue实现大顶堆

private static final int DEFAULT_INITIAL_CAPACITY = 11;
PriorityQueue<Integer> maxHeap=new PriorityQueue<Integer>(DEFAULT_INITIAL_CAPACITY, new Comparator<Integer>() {
        @Override
        public int compare(Integer o1, Integer o2) {                
            return o2-o1;
        }
    });

例子：输入n个整数，找出其中最小的K个数。例如输入4,5,1,6,2,7,3,8这8个数字，则最小的4个数字是1,2,3,4,可以使用大顶堆保存，比堆中的数小就进堆。

import java.util.ArrayList;
import java.util.PriorityQueue;
import java.util.Comparator;
public class Solution {
   public ArrayList<Integer> GetLeastNumbers_Solution(int[] input, int k) {
       ArrayList<Integer> result = new ArrayList<Integer>();
       int length = input.length;
       if(k > length || k == 0){
           return result;
       }
        PriorityQueue<Integer> maxHeap = new PriorityQueue<Integer>(k, new Comparator<Integer>() {
 
            @Override
            public int compare(Integer o1, Integer o2) {
                return o2.compareTo(o1);
            }
        });
        for (int i = 0; i < length; i++) {
            if (maxHeap.size() != k) {
                maxHeap.offer(input[i]);
            } else if (maxHeap.peek() > input[i]) {
                Integer temp = maxHeap.poll();
                temp = null;
                maxHeap.offer(input[i]);
            }
        }
        for (Integer integer : maxHeap) {
            result.add(integer);
        }
        return result;
    }
}