Kth Largest Element in an Array 解答

Question

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.

Solution 1 -- PriorityQueue

 1 public class Solution {
 2     public int findKthLargest(int[] nums, int k) {
 3         if (nums == null || k > nums.length)
 4             return 0;
 5         int length = nums.length, index = length - k, result = 0;
 6         PriorityQueue<Integer> pq = new PriorityQueue<Integer>(length,
 7                                                             new Comparator<Integer>(){
 8                                                                 public int compare(Integer a, Integer b) {
 9                                                                     return (a - b);
10                                                                 }
11                                                             });
12         for (int i = 0; i < length; i++)
13             pq.add(nums[i]);
14         while (index >= 0) {
15             result = pq.poll();
16             index--;
17         }
18         return result;
19     }
20 }

Solution 2 -- Quick Select

Quick Sort in Java