LeetCode 215: Kth Largest Element in an Array

class Solution {
    public int findKthLargest(int[] nums, int k) {
        if (nums.length == 0) {
            return 0;
        }
        return findKth(nums, 0, nums.length - 1, nums.length - k);
    }
    
    private int findKth(int[] nums, int start, int end, int k) {
        if (start > end) {
            return -1;
        }
        int pivot = nums[end];
        int runner = start;
        for (int i = start; i < end; i++) {
            if (nums[i] <= pivot) {
                swap(nums, i, runner++);
            }
        }
        
        swap(nums, runner, end);
        
        if (runner == k) {
            return nums[runner];
        } else if (runner < k) {
            return findKth(nums, runner + 1, end, k);
        }
        return findKth(nums, start, runner - 1, k);
    }
    
    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
}