java - 如何打印给定范围内以1结尾的素数以及b之后最接近的素数？

Question

• 示例输入: 10 100

• 示例输出: 11,31,41,61,71,101

• 从上面的代码中我可以获得最大为71的样本输出值，如何获得b后面以1结尾的最接近的素数。

这是我尝试过的代码:

import java.util.*;
public class Program{
public static void main(String[] args){
    Scanner in=new Scanner(System.in);
    int a=in.nextInt();
    int b=in.nextInt();
    int i,j,count;
    for(i=a;i<=b;i++)
    {
        for(j=2;j<=b;j++)
        {
            if(i%j==0)
            break;
        }
        if(j==i && j%10==1) 
        {
            System.out.println(i);
        }
    }
} 

Answer 1

您不需要将一个数字除以它之前的数字来检查它是否是素数。您只需检查其平方根即可。检查https://en.wikipedia.org/wiki/Primality_test 。执行如下操作:

使用for循环

import java.util.Scanner;

public class Program {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);
        System.out.print("Enter two integers separated by space: ");
        int a = in.nextInt();
        int b = in.nextInt();
        int i, j, sqrt;

        // Note that there are three sections in the declaration of a 'for' loop:
        // for(initialization;condition;change) where none of the sections is
        // mandatory. There is no condition put in the loop syntax given below. The
        // condition for termination has been put after printing the prime number.
        for (i = a;; i++) {
            sqrt = (int) Math.sqrt(i);
            for (j = 2; j <= sqrt; j++) {
                if (i % j == 0) {
                    break;
                }
            }
            // If the loop with j completed without a break, the number is prime. Note that
            // 1 is not a prime number.Also, the last digit of the number should be 1.
            if (j > sqrt && Math.abs(i) != 1 && i % 10 == 1) {
                System.out.print(i + " "); // Print the prime
                if (i >= b) {// Condition for termination
                    break;
                }
            }
        }
    }
}

或者，使用 while 循环

import java.util.Scanner;

public class Program {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);
        System.out.print("Enter two integers separated by space: ");
        int a = in.nextInt();
        int b = in.nextInt();
        int i = a, j, sqrt;

        while (true) {
            sqrt = (int) Math.sqrt(i);
            for (j = 2; j <= sqrt; j++) {
                if (i % j == 0) {
                    break;
                }
            }
            // If the loop with j completed without a break, the number is prime. Note that
            // 1 is not a prime number.Also, the last digit of the number should be 1.
            if (j > sqrt && Math.abs(i) != 1 && i % 10 == 1) {
                System.out.print(i + " "); // Print the prime
                if (i >= b) {// Condition for termination
                    break;
                }
            }
            i++;
        }
    }
}

示例运行:

Enter two integers separated by space: 10 100
11 31 41 61 71 101

另一个示例运行:

Enter two integers separated by space: 10 200
11 31 41 61 71 101 131 151 181 191 211