我现在正在大学里学习DFA和NFA自动机,以及如何使用Java代码实现其中的一些自动机。
我在进行此练习时遇到了一些麻烦:我们有4个不同的实验室回合(T1,T2,T3和T4),我们需要编写代码以识别是否有特定的字符串(由a的大学徽章编号组成)学生及其名字,例如123321Johnson
)对应于T2或T3。
我们知道:
我们还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"
或"1232323Lum"
,但不能接受"121234Lum"
或"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");
}
}
很显然,该代码无法正常工作,但这对于表明练习的一般目的很重要。
有人可以帮我吗?
答案 0 :(得分:0)
您的算法无法正常运行的原因是,您试图将char
的值与int
的值进行比较,但无法给出预期的结果。另外,当您检查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
{
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:
// Compare the char to the char values of the numbers
if (ch >= '0' && ch <= '9')
state = 1;
else
state = -1;
break;
case 1:
// Same here, compare the char to the char values of the numbers
if (ch >= '0' && ch <= '9')
state = 1;
// Check if the char is capital, as well as lowercase
else if ((ch >= 'a' && ch <= 'k') || (ch >= 'A' && ch <= 'K'))
// Convert the char to an int before performing the calculations
if ((Character.getNumericValue(s.charAt(i-1)))%2 == 0)
state = 2;
else
state = -1;
// Check if the char is capital as well
else if ((ch >= 'l' && ch <= 'z') || (ch >= 'L' && ch <= 'Z'))
// Convert from char to int before calculating
if ((Character.getNumericValue(s.charAt(i-1)))%2 == 1)
state = 3;
else
state = -1;
else
state = -1;
break;
case 2:
// Check if the char is capital as well
if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))
state = 2;
else
state = -1;
break;
case 3:
// Check if the char is capital as well
if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))
state = 3;
else
state = -1;
break;
}
}
System.out.println("State "+state);
return (state == 2 || state == 3);
}
public static void main(String[] args)
{
System.out.println(scan(args[0]) ? "OK" : "NO");
}
}
我认为上面的代码应该可以完成您想做的事情。