快排及寻找第k小的值（前k小的值）

package sort;

import java.util.Arrays;

public class QuikSort {

	public static int[] quickSort(int[] arr) {
		int length = arr.length;
		sort(arr, 0, length - 1);
		return arr;
	}

	public static void sort(int[] arr, int left, int right) {
		if (left > right) {
			return;
		}
		int index = partation(arr, left, right);
		sort(arr, left, index - 1);
		sort(arr, index + 1, right);

	}

	public static int partation(int[] arr, int left, int right) {

		int temp = arr[left];
		int i = left + 1;
		int j = right;
		while (true) {
			while (arr[i] <= temp && i < right) {
				i++;
			}
			while (arr[j] >= temp && j > left) {
				j--;
			}
			if (i >= j)
				break;
			swap(arr, i, j);
		}
		swap(arr, left, j);
		return j;
	}

	public static void swap(int[] arr, int i, int j) {
		int temp = arr[i];
		arr[i] = arr[j];
		arr[j] = temp;
	}

	public static void main(String[] args) {
		int[] arr = { 3, 6, 9, 2,10, 8, 67, 7, 1 };
		//System.out.println(Arrays.toString(quickSort(arr)));
		findK(arr,5);
		System.out.println(Arrays.toString(arr));
	}

	
	/*********************************************************************************************/
	// 寻找第K小元素或者说前k小的元素
	public static void findK(int[] arr, int k) {
		int length = arr.length;
		int i = 0;
		int j = length - 1;
        int index = partation(arr,i,j);
        while((index!=k-1)){
        	if(index<k-1){
        		index =partation(arr,index+1,j);
        	}else{
        		index = partation(arr,i,index-1);
        	}
        }
        System.out.println(arr[k-1]);
	}
	
	
	// 寻找第K小元素或者说前k小的元素
		public static void findK2(int[] arr, int k) {
			int length = arr.length;
			int i = 0;
			int j = length - 1;
			int[] output = new int[k];
	        while(j>i){
	        	int position= partation(arr,i,j);
	        	if(position==k){
	        		System.out.println(arr[k]);
	        		//return arr[k-1];
	        	}else if(position<k){
	        		i = position+1;
	        	}else{
	        		j= position-1;
	        	}
	        }
	        //这里的K是数组的K,而不是第k个要减一
	        System.out.println(arr[k]);
	       // return arr[k-1];
		}
}