Question

我是Java的一个完全初学者，刚刚介绍了循环。我试着写一个读入目标的程序并找到第一个n，使得1 + 1/2 + 1/3 + ... + 1 / n>目标。该问题提供了一个代码，其初始化为n和sum，以及while及其语句缺失的情况。

我能够弄清楚如何制作谐波系列循环，但我不知道在超过目标时如何设置n来停止循环。我们还没学会关于类中的数组..

import java.util.Scanner;

/**
 This program computes how many steps the sum 1 + 1/2 + 1/3 + ...
 needs to exceed a given target. 
 */
public class ReciprocalSum
{
    public static void main(String[] args)
    {  

        double sum = 0;
        int n = ????  ;

        Scanner in = new Scanner(System.in);
        System.out.print("Target: ");
        double target = in.nextDouble();
        int i = 0; 

//Notes 
        // 1 + 1/2 + 1/3 + 1/4 + ..... 1/n 
        //Make a loop that repeats itself starting with n = 1 --> 1/1 + 1/2 + 1/3 + 1/4 + 1/n 

        // 1.0/n + (1.0/ n - 1) + (1.0/n-2) +.... if n =4 --> 1/4 + 1/3 + 1/2 + 1/1 as long as n >0 


        while ( n > 0) 
        {  
            sum += 1.0/n ;
            n--; 
        }

        System.out.println("n: " + n);
        System.out.println("sum: " + sum);
    }
}

Answer 1

n应该在循环中递增（因此它应该从0开始），当你到达目标时应该退出循环：

int n = 0;

...

while (sum <= target) 
{  
    n++;
    sum += 1.0/n;
}

Answer 2

因为Java 8+具有lambda，并且您可以生成范围1到n并执行计算并一步获得总和。基本上，你可以做到

Scanner in = new Scanner(System.in);
System.out.print("Target: ");
double target = in.nextDouble(), sum = 1.0;
int n = 1;
while (sum < target) {
    sum = IntStream.range(1, n).mapToDouble(i -> 1.0 / i).sum();
    n++;
}
System.out.printf("n=%d, sum=%.2f%n", n, sum);

Answer 3

你可以通过计算系列的Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/spark/mllib/recommendation/Rating at java.lang.Class.getDeclaredMethods0(Native Method) at java.lang.Class.privateGetDeclaredMethods(Class.java:2625) at java.lang.Class.getMethod0(Class.java:2866) at java.lang.Class.getMethod(Class.java:1676) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:126) Caused by: java.lang.ClassNotFoundException: org.apache.spark.mllib.recommendation.Rating at java.net.URLClassLoader$1.run(URLClassLoader.java:359) at java.net.URLClassLoader$1.run(URLClassLoader.java:348) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:347) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:312) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) ... 5 more Process finished with exit code 1来实现这一点，直到它的总和大于目标值：

sum

如何在达到Java中的指定目标时停止对谐波系列求和？

3 个答案: