找到第K大的数

import java.util.*;

public class Finder {
    private void swap(int[] a, int i, int j) {
        int temp = a[i];
        a[i] = a[j];
        a[j] = temp;
    }
    private int getIndex(int[] a, int l, int r) {
        int left = l, right = r;
        int pivot = a[l];
        while(l <= r) {
            while(l <= r && a[l] <= pivot) l ++;
            while(l <= r && a[r] >= pivot) r --;
            if(l <= r) {
                swap(a, l, r);
            }
        }
        swap(a, left, r);
        return r;
    }
    private int quickSort(int[] a, int k, int l, int r) {
        int n = a.length;
        int index = getIndex(a, l, r);
        
        if(index == n - k) {
            return a[index];
        } else if(index > n - k -1) {
            return quickSort(a, k, l, index - 1);
        } else {
            return quickSort(a, k, index + 1, r);
        }
    }
    public int findKth(int[] a, int n, int K) {
        // write code here
        if(a == null) return -1;
        return quickSort(a, K, 0, a.length - 1);
    }
}