automata, check string is accepted by language | C++

Question

This is my automata, and it Regular Expression for this language is (aaa*b|ba)a*

I want to make a C++ program for check input string is accepted by this language or not.

This program get the string and print Accepted or Rejected

For example:

input: aaaba - output: Accepted

input: baa - output: Accepted

input: aaa - output: Rejected

Answer 1

#include <string>
#include <iostream>

bool check_string(const std::string& s) {
  static constexpr int INV = -1;
  static constexpr int INITIAL_STATE = 0;
  static constexpr int ACCEPTING_STATE = 3;
  static const int transition_table[5][2] = {
    //  a    b
    {   1,   2   },  // 0
    {   4,  INV  },  // 1
    {   3,  INV  },  // 2
    {   3,  INV  },  // 3
    {   4,   3   }   // 4
  };

  int state = INITIAL_STATE;
  for (char c : s) {
    if (c != 'a' && c != 'b') return false;
    state = transition_table[state][c - 'a'];
    if (state == INV) return false;
  }
  return state == ACCEPTING_STATE;
}

int main(int argc, char* argv[]) {
  if (argc != 2) {
    std::cerr << "Usage: check str\n";
    return 1;
  }
  if (check_string(argv[1]))
    std::cout << "Accepted\n";
  else
    std::cout << "Rejected\n";
  return 0;
}