如何识别哪些正则表达式匹配是素数？

Question

我有一个文本文件和一个正则表达式，它可以提取整个文本中写入的所有数字。我能够匹配和提取这些数字，但我在尝试识别哪些提取的数字是素数时遇到了麻烦。

有人可以帮我吗？谢谢！

这是我的代码：

import java.util.Scanner;//Import Scanner class to read a file in the computer
import java.io.File;//Import File class to read a file in the computer
import java.io.FileNotFoundException;//Import FileNotFoundException class if case file is not found in the computer

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Regex2 {
    public static void main(String[] args) throws FileNotFoundException {        
        int count = 0;
        //Display each word in INPUT_TEXT
        Scanner INPUT_TEXT = new Scanner(new File("/Users/Matt/Desktop/regex2.csv"));//Create a Scanner Class and File Class to read a file from your computer.

        INPUT_TEXT.useDelimiter(" ");//Divide file into several pieces by a space  
        if (INPUT_TEXT != null) {
            System.out.println(INPUT_TEXT);
        }

        while(INPUT_TEXT.hasNext()) {
            //Read each word
            String TempString = INPUT_TEXT.next();
            //Display all numbers.Eliminate comma, e.g., 1,200 -> 1200
            String temp1 = TempString.replaceAll("[\\,]", "");//Create a String class temp1 that eliminates comma.
            String pattern1 = "[0-9]+";//Create a String class pattern1 that stores the Regular Expression to match numbers.

            Pattern r1 = Pattern.compile(pattern1);//Create Pattern class to compile pattern1.

            Matcher m1 = r1.matcher(temp1);//Match each piece with the Regular Expression

            if (m1.find()) {   
                System.out.print(m1.group() + " ");
                //System.out.println(count);
                count++;
            // if count reaches 5, reset count and print new line
            if (count == 5) {
                count = 0;
                System.out.println();
            }
        }
    }
    INPUT_TEXT.close();//Close your Scanner.
    }
}

Answer 1

您完全误解了您链接到的帖子。看起来您有一个表示数字的字符串，并且您认为可以使用正则表达式来确定它是否为素数。这是完全不可能的。

这篇文章展示了如何通过创建一个长度为 n 的字符串来测试 n 是否为素数，并将其与仅当字符串可以分解为 2 时才匹配的正则表达式匹配或更多长度相等且长度> = 2的组。如果可以，则该数字不能是素数，因为它必须是> = 2的两个数字的乘积。这是测试素数的一种非常糟糕的方法.唯一的用途就是让一些人炫耀自己的聪明才智。

即使您确实创建了该长度的字符串，您的代码也不会工作，因为您使用的是find()，如果您的源字符串的任何子字符串匹配，它将成功。这行不通。这个技巧只有在匹配器被强制匹配整个源字符串时才有效。

Answer 2

如果您可以使用 一元 格式的数字。

你可以参考这个link

Answer 3

是的，我所要做的就是添加另一个“isPrime”方法。尽管我将每个匹配项添加到数组列表中，但我相信您也可以将 group(0) 解析为 Integer 并像这样测试每个值。

这是我的代码：

import java.util.Scanner;//Import Scanner class to read a file in the computer
import java.io.File;//Import File class to read a file in the computer
import java.io.FileNotFoundException;//Import FileNotFoundException class if case file is not found in the computer

import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.*; // Import all java utilities


public class assignmentTwo {
    public static ArrayList<Integer> nums;

    public static void main(String[] args) throws FileNotFoundException{

        int count = 0;


        //Display each word in INPUT_TEXT
        Scanner INPUT_TEXT = new Scanner(new File("/Users/Matt/Desktop/assignment2.csv"));//Create a Scanner Class and File Class to read a file from your computer.


        INPUT_TEXT.useDelimiter(" ");//Divide DemoData.txt into several pieces by a space

        // test to see if file was received
        if (INPUT_TEXT != null) {

            System.out.println(INPUT_TEXT);

        }


        while(INPUT_TEXT.hasNext()){


            //Read each word
            String TempString = INPUT_TEXT.next();

            //Display all numbers.Eliminate comma, e.g., 1,200 -> 1200
            String temp1 = TempString.replaceAll("[\\,]", "");//Create a String class temp1 that eliminates comma.
            String pattern1 = "[0-9]+";//Create a String class pattern1 that stores the Regular Expression to match numbers.
            Pattern r1 = Pattern.compile(pattern1);//Create Pattern class to compile pattern1.
            Matcher m1 = r1.matcher(temp1);//Match each piece with the Regular Expression


            // array variable
            nums = new ArrayList<Integer>();

            // find values that match
            if (m1.find( )) {

            // parse array values from string to integers
            int parsedNum = Integer.parseInt(m1.group());
            nums.add(parsedNum);


            //If a number is matched, print the number.
            System.out.print(m1.group() + " ");

            // increment counter when number validation is reached
            count++;


            // if count reaches 5, reset count and print new line
            if (count == 5) {

            count = 0;

            System.out.println();



    }

    // run isPrime method
     isPrime();

}

    }

        INPUT_TEXT.close();//Close your Scanner.

    }

    // isPrime method to test which #s are prime
    public static int isPrime(){

        // finds size of array
        for(int s = 0; s < nums.size(); s++){

            // primeNum is true by default
            boolean primeNum = true;

            /* if a value from the array is divisible by any # <= array value
                then that value is not prime */
            for (int divisor = 2; divisor <= nums.get(s) / 2; divisor++) {
                if (nums.get(s) % divisor == 0) {

                    primeNum = false;

                }

            }
                // if value is prime, print out current value 
                if (primeNum) {

                    //System.out.println();
                    System.out.print(nums.get(s) + " ");

                    // return array list values
                    return nums.get(s);

                }

        }

        // exit status
        return 0;
    }    
}