题解 | 随机序列

import java.util.Scanner;
import java.util.Arrays;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int T = in.nextInt();
        for (int i = 0 ; i < T ; i++) {
            int x = in.nextInt();
            int[] nums = new int[x];
            for (int j = 0 ; j < x ; j++) {
                nums[j] = in.nextInt();
            }
            System.out.printf("%d %.3f\n",abc( nums ),def( nums ));
        }
    }
    public static int abc(int[] nums) {
        int a = 0, b = 5001;
        for (int i = 0; i < nums.length ; i++) {
            if ( a < nums[i]) {
                a = nums[i];
            }
            if ( b > nums[i]) {
                b = nums[i];
            }
        }
        return a - b;
    }
    public static double calculateAverage(int[] array) {
        if (array == null || array.length == 0) {
            return 0.0;
        }
        return Arrays.stream(array)
               .average()      
               .orElse(0.0); 
    }
    public static double def(int[] nums) {
        double sum = 0.0;
        double x = calculateAverage(nums);
        for (int i = 0 ; i < nums.length ; i++)
        {
            sum += (nums[i] - x)*(nums[i] - x);
        }
        return sum / nums.length;
    }

}