有效帕斯卡标识符的识别器
原文:https://www . geeksforgeeks . org/DFA-identifier-for-valid-Pascal-identifier/
问题–基于接受属于同一语言定义的字符串的 DFA，实现帕斯卡标识符的识别器。
这里是帕斯卡标识符集合的常规定义，帕斯卡标识符被定义为以字母开头的字母和数字串的集合。
letter : A | B | . . . | Z | a | b | . . . | z
digit : 0 | 1 | 2 | . . . | 9
ID : letter (letter | digit)*
正则表达式标识是帕斯卡标识符令牌的模式，定义了字母和数字，其中字母是字母表中所有大小写字母集合的正则表达式，数字是所有十进制数字集合的正则表达式。
DFA 状态图
识别器的工作代码:
C++
// C++ program to implement DFA based regonizer that accepts
// all strings which follow the language
// L = { letter (letter | digit)* }
#include <bits/stdc++.h>
#include <iostream>
using namespace std;
// dfa tells the number associated
// with the present state
int dfa;
// This function is for
// the starting state (zeroth) of DFA
void start(char c)
{
if (isalpha(c))
dfa = 1;
else
// -1 is used to check for any invalid symbol
dfa = -1;
}
// This function is for the first state of DFA
void state1(char c)
{
if (isalnum(c))
dfa = 1;
else
dfa = -1;
}
bool DFA_for_ID(string token)
{
dfa = 0;
int i, len = token.length();
for (i = 0; i < len; i++) {
if (dfa == 0)
start(token[i]);
else if (dfa == 1)
state1(token[i]);
else
return 0;
}
if (dfa == 1)
return 1;
else
return 0;
}
// driver code
int main()
{
string input = "Geeks for Geeks is 9ice platfo$m for every1 ";
// to separate all the tokens by space in the string
// and checking for each token
stringstream ss(input);
string token;
while (ss >> token) {
bool isValid = DFA_for_ID(token);
if (isValid)
cout << token << " : "
<< "Valid" << endl;
else
cout << token << " : "
<< "Invalid" << endl;
}
return 0;
}
输出:
Geeks : Valid
for : Valid
Geeks : Valid
is : Valid
9ice : Invalid
platfo$m : Invalid
for : Valid
every1 : Valid
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