JAVA 代码

import java.util.Scanner;
import java.io.BufferedInputStream;

class Main{
    public static void main(String[] args) {
        Scanner in = new Scanner(new BufferedInputStream(System.in));
        int n = in.nextInt();
        int q = in.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = in.nextInt();
        }

        MergeSort(arr, 0, n - 1);

        System.out.println(find(arr, q - 1));
    }
    public static int find(int[] arr, int k){
        return arr[k];
    }
    public static void quickSort(int[] arr, int l, int r){
        if(l >= r)
            return;
        //1. 确定分界点
        int x = arr[l];
        int i = l - 1, j = r + 1;
        //2. 分区间
        while(i < j){
            do i++; while(arr[i] < x);
            do j--; while(arr[j] > x);
            if(i < j){
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
        //3. 递归
        quickSort(arr, l, j);
        quickSort(arr, j + 1, r);
    }

    public static void MergeSort(int[] arr, int l, int r){
        if(l >= r)
            return;
        //0. 确定分界点---取中点
        int mid = l + r >> 1;
        //1. 递归排序左边和右边
            MergeSort(arr, l, mid);
            MergeSort(arr, mid + 1, r);
        //2. 归并---将两个有序数组合并成一个有序数组---双指针算法
        //对两个数组分别取头指针，不断比较两个指针大小，在开辟一个新数组容纳
        int[] temp = new int[r - l + 1];
        int k = 0;//表示当前temp一共有多少个数
        int i = l,j = mid + 1 ;//两个指针
        while(i <= mid && j <= r){
            if(arr[i] <= arr[j])
                temp[k++] = arr[i++];
            else
                temp[k++] = arr[j++];
        }
        while(i <= mid)
            temp[k++] = arr[i++];
        while(j <= r)
            temp[k++] = arr[j++];
        for (i = l, j = 0; i <= r; i++, j++)
            arr[i] = temp[j];
    }
}