自动机 DFA 实现无法使用 Java

Question

我现在正在我的大学学习 DFA 和 NFA 自动机以及如何使用 Java 代码实现其中的一些。

我在这个练习中遇到了一些麻烦：我们有 4 个不同的实验室回合（T1、T2、T3 和 T4），我们需要编写代码来识别特定的字符串（由学生的大学徽章编号和他的名称，例如，123321Johnson) 对应于 T2 或 T3。

我们知道：

• T1 轮到徽章编号和姓氏在“A”和“K”之间的奇数

• T2是“A”和“K”之间偶数徽章数字和姓氏的轮换

• T3是“L”和“Z”之间的奇数徽章号码和姓氏的轮换

• T4是“L”和“Z”之间偶数徽章数字和姓氏的轮换

我们也知道字符串必须由至少一个数字和至少一个字母组成。

例如，自动机必须接受"1232324Gac"or"1232323Lum"但不接受"121234Lum"or "121233Gac"。

这是我写的代码：

import java.util.Scanner;

public class Es3 {

    static Scanner sc = new Scanner(System.in);

    String s = sc.next();

    public static boolean scan(String s)

    {

        int state = 0;                      

        int i = 0;                              

        while (state >= 0 && i < s.length()) {

            final char ch = s.charAt(i++);

            switch (state) {

            case 0:

                if (ch >= 0 && ch <= 9)

                    state = 1;

                else

                    state = -1;

                break;

            case 1:

                if (ch >=0 && ch <=9)

                    state = 1;

                else if (ch >='a' && ch <='k')

                    if ((s.charAt(i--))%2==0)

                        state = 2;

                    else

                        state = -1;

                else if (ch >='l' && ch <='z')

                    if ((s.charAt(i--))%2==1)

                        state = 3;

                    else

                        state = -1;

                else

                    state = -1;

                break;

            case 2:

                if (ch >='a' && ch <='z')

                    state = 2;

                else

                    state = -1;

                break;

            case 3:

                if (ch >='a' && ch <='z')

                    state = 3;

                else 

                    state = -1;

                break;

            }

        }

        return (state == 2 || state == 3);      

    }

    public static void main(String[] args)

    {

        System.out.println(scan(args[0]) ? "OK" : "NO");

    }

}

显然，代码不起作用，但这对于展示练习的一般目的很重要。

有人可以帮助我吗？

Answer 1

您的算法不起作用的原因是因为您试图将char值与int值进行比较，这不会给出预期的结果。此外，当您检查某个char值是否在某个字母范围内时，您没有考虑大写字母。import java.util.Scanner;public class Es3&nbsp;{&nbsp; &nbsp; static Scanner sc = new Scanner(System.in);&nbsp; &nbsp; String s = sc.next();&nbsp; &nbsp; public static boolean scan(String s)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; int state = 0;&nbsp; &nbsp; &nbsp; &nbsp; int i = 0;&nbsp; &nbsp; &nbsp; &nbsp; while (state >= 0 && i < s.length()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; final char ch = s.charAt(i++);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; switch (state) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; case 0:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Compare the char to the char values of the numbers&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (ch >= '0' && ch <= '9')&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = 1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; else&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = -1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; case 1:&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Same here, compare the char to the char values of the numbers&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (ch >= '0' && ch <= '9')&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = 1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Check if the char is capital, as well as lowercase&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; else if ((ch >= 'a' && ch <= 'k') || (ch >= 'A' && ch <= 'K'))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Convert the char to an int before performing the calculations&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if ((Character.getNumericValue(s.charAt(i-1)))%2 == 0)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = 2;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; else&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = -1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Check if the char is capital as well&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; else if ((ch >= 'l' && ch <= 'z') || (ch >= 'L' && ch <= 'Z'))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Convert from char to int before calculating&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if ((Character.getNumericValue(s.charAt(i-1)))%2 == 1)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = 3;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; else&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = -1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; else&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = -1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; case 2:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Check if the char is capital as well&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = 2;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; else&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = -1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; case 3:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Check if the char is capital as well&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = 3;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; else&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; state = -1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; System.out.println("State "+state);&nbsp; &nbsp; &nbsp; &nbsp; return (state == 2 || state == 3);&nbsp; &nbsp; &nbsp;&nbsp;&nbsp; &nbsp; }&nbsp; &nbsp; public static void main(String[] args)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(scan(args[0]) ? "OK" : "NO");&nbsp; &nbsp; }}我认为上面的代码应该做你想做的事情。