题解 | 最小的K个数

import java.util.*;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.PriorityQueue;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param input int整型一维数组
     * @param k int整型
     * @return int整型ArrayList
     */
    public ArrayList<Integer> GetLeastNumbers_Solution (int[] input, int k) {
        if (k == 0 || input.length == 0) {
            return new ArrayList<>();
        }

        PriorityQueue<Integer> pq = new PriorityQueue<>(k, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o2 - o1;
            }

        });
        for (int i = 0; i < input.length; i++) {
            if (pq.size() < k) {
                pq.add(input[i]);
            } else {
                Integer peek = pq.peek();
                if (peek > input[i]) {
                    pq.poll();
                    pq.add(input[i]);
                }
            }
        }
        ArrayList<Integer> result = new ArrayList<>(pq.size());

        Stack<Integer> stack = new Stack<>();
        while (!pq.isEmpty()) {
            stack.push(pq.poll());
        }
        while (!stack.isEmpty()) {
            result.add(stack.pop());
        }
        return result;
    }
}