Leetcode 215. Kth Largest Element in an Array

215. Kth Largest Element in an Array

Total Accepted: 81842 Total Submissions: 226913 Difficulty: Medium

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.

For example,
Given [3,2,1,5,6,4] and k = 2, return 5.

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

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

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 (M) Wiggle Sort II (M) Top K Frequent Elements

思路：

看到top kth，直接反应就是heap。

用一个最大堆，然后放入元素，第K次取的元素就是所求。

运行时间：16ms。

public class Solution {    public int findKthLargest(int[] nums, int k) {        PriorityQueue<Integer> heap = new PriorityQueue<Integer>(Collections.reverseOrder());        for(int item : nums) heap.offer(item);                int count = 0;        while(count < k){            int item = heap.poll();            count++;            if(count == k) return item;        }        return -1;    }}

然后一看标签是分治。那好现在nums的k，就等于nums删除最大元素的k -1，直到k==1。

于是最后一定是最大元素。于是一定要sort。那么sort之后直接无视分治取出相应位置元素就可以了。

运行时间：5ms。

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