LeetCode71|数组中第K个最大元素

示例 1:

输入: [3,2,1,5,6,4] 和 k = 2
输出: 5
示例 2:

输入: [3,2,3,1,2,4,5,5,6] 和 k = 4
输出: 4
说明:

你可以假设 k 总是有效的，且 1 ≤ k ≤ 数组的长度。

 
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class FindKthLargestTest2 {
    public static void main(String[] args) {
        int[] nums = {3, 2, 1, 5, 6, 4};
        int k = 2;
        int kthLargest = findKthLargest2(nums, k);
        System.out.println("kthLargest = " + kthLargest);
    }

    public static int findKthLargest(int[] nums, int k) {
        if (nums == null || nums.length == 0 || nums.length < k) {
            return -1;
        }
        Arrays.sort(nums);
        List<Integer> list = new ArrayList<>();
        for (int j : nums) {
            list.add(j);
        }
        Collections.sort(list, Comparator.reverseOrder());

        return list.get(k - 1);
    }

    public static int findKthLargest2(int[] nums, int k) {
        if (nums == null || nums.length == 0 || nums.length < k) {
            return 0;
        }

        PriorityQueue<Integer> priorityQueue = new PriorityQueue<>(k);
        for (Integer num : nums) {
            if (priorityQueue.size() < k || num > priorityQueue.peek()) {
                priorityQueue.offer(num);

            }
            if (priorityQueue.size() > k) {
                priorityQueue.poll();
            }
        }

        return priorityQueue.peek();
    }
}