215. Kth Largest Element in an Array

Posted 2020-07-21 蜃利的阴影下

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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1. Quick Select Algorithm:

https://en.wikipedia.org/wiki/Quickselect

 

2. Priority Queue:

public class Solution {
    public int findKthLargest(int[] nums, int k) {
        PriorityQueue<Integer> pq = new PriorityQueue<Integer>(k);
        
        for(int i : nums)
        {
            if(pq.size() < k)
                pq.add(i);
            else if(pq.peek() < i)
            {
                pq.remove();
                pq.add(i);
            }
        }
        
        return pq.peek();
    }
}