【leetcode】215. Kth Largest Element in an Array

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.

題解如下：

思路1：利用排序

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

思路2：利用優先級隊列

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