LeetCode34|数组中的第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;

public class FindKthLargestTest {
    public static void main(String[] args) {
        int[] array = {3, 2, 1, 5, 6, 4};

        int k = 2;
        int kthLargest = findKthLargest(array, k);
        System.out.println("kthLargest = " + kthLargest);
        int kthLargest2 = findKthLargest2(array, k);
        System.out.println("kthLargest2 = " + kthLargest2);
    }

    public static int findKthLargest(int[] nums, int k) {
        if (nums == null || nums.length == 0 || nums.length < k) {
            return -1;
        }

        ArrayList<Integer> arrayList = Arrays.stream(nums).boxed().sorted(Comparator.reverseOrder()).collect(Collectors.toCollection(ArrayList::new));
        return arrayList.get(k - 1);
    }

    public static int findKthLargest2(int[] nums, int k) {
        if (nums == null || nums.length == 0 || nums.length < k) {
            return -1;
        }
        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();
    }
}