快排和TopK

import java.util.*;
public class Main{
    public static void main(String[] args){
        int arr[] = {6,2,7,1,3,5,6};
        int res = findKthLarge(arr,0,arr.length-1, 4);
        System.out.println(res);
    }

    private static int findKthLarge(int arr[], int left, int right, int k){
        int pos = partition(arr, left, right);
        int rightLen = right-pos+1;
        if (rightLen==k)
            return arr[pos];
        else if (rightLen>k)
            return findKthLarge(arr, pos+1, right, k);
        else
            return findKthLarge(arr, left, pos-1, k-rightLen);
    }

    private static int partition(int arr[], int left, int right){
        int pivot = arr[left];
        while (left<right){
            while (left<right && arr[right]>=pivot)
                right--;
            swap(arr, left, right);
            while (left<right && arr[left]<pivot)
                left++;
            swap(arr, left, right);
        }
        arr[left] = pivot;
        return left;
    }

    private static void swap(int arr[], int a, int b){
        int temp = arr[a];
        arr[a] = arr[b];
        arr[b] = temp;
    }
}