[LC] 215. Kth Largest Element in an Array

Posted 2020-11-22 xuanlu

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

Example 1:

Input: [3,2,1,5,6,4] and k = 2
Output: 5

Example 2:

Input: [3,2,3,1,2,4,5,5,6] and k = 4
Output: 4

Note:
You may assume k is always valid, 1 ≤ k ≤ array‘s length.

 

Solution 1: 

Time: O(NlgN)

class Solution {
    public int findKthLargest(int[] nums, int k) {
        Arrays.sort(nums);
        return nums[nums.length - k];
    }
}

 

Solution 2:

Time: O(Nlgk)

class Solution {
    public int findKthLargest(int[] nums, int k) {
        if (nums == null || nums.length == 0) {
            return 0;
        }
        PriorityQueue<Integer> pq = new PriorityQueue<>();
        for (int num : nums) {
            pq.offer(num);
            if (pq.size() > k) {
                pq.poll();
            }
        }
        return pq.poll();
    }
}