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.

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.

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

=======

public class Solution {
   
    private int partition(int[] nums, int from, int to) {
        java.util.Random r = new java.util.Random();
        int idx = from + r.nextInt(to - from + 1);
        swap(nums, idx, to);
        int start = from;
        for (int i = from; i < to; i++) {
            if (nums[i] < nums[to]) {
                swap(nums, start, i);
                start++;
            }
        }
        swap(nums, to, start);
        return start;
    }
   
    private void swap(int nums[], int p, int q) {
        int tmp = nums[p];
        nums[p] = nums[q];
        nums[q] = tmp;
    }
   
    private int quickSelect(int[] nums, int k) {
        int s = 0;
        int e = nums.length - 1;
        while (s <= e) {
            int m = partition(nums, s, e);
            if (m == k) {
                return nums[m];
            } else if (m < k) {
                s = m + 1;
            } else {
                e = m - 1;
            }
        }
        return 0;
    }
   
    public int findKthLargest(int[] nums, int k) {
        return quickSelect(nums, nums.length - k);
    }
}