InfiniteLanguage.h

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/*
 * This file is part of Algorithms library toolkit.
 * Copyright (C) 2017 Jan Travnicek (jan.travnicek@fit.cvut.cz)
 
 * Algorithms library toolkit is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 
 * Algorithms library toolkit is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 
 * You should have received a copy of the GNU General Public License
 * along with Algorithms library toolkit.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include <queue>
#include <set>
 
#include <automaton/FSM/NFA.h>
#include <automaton/FSM/DFA.h>
 
#include <automaton/properties/UsefulStates.h>
 
namespace automaton {
 
namespace properties {
 
class InfiniteLanguage {
public:
    template < class T >
    requires isDFA < T > || isNFA < T >
    static bool infinite ( const T & fsm );
};
 
template < class T >
requires isDFA < T > || isNFA < T >
bool InfiniteLanguage::infinite ( const T & fsm ) {
    using StateType = typename T::StateType;
 
    const ext::set < StateType > usefulStates = automaton::properties::UsefulStates::usefulStates ( fsm );
 
    std::queue < StateType > q;
    std::set < StateType > visited { fsm.getInitialState ( ) };
 
    q.push ( fsm.getInitialState ( ) );
 
    while ( ! q.empty ( ) ) {
        const StateType state = std::move ( q.front ( ) );
        q.pop ( );
 
        for ( const auto & transition : fsm.getTransitionsFromState ( state ) ) {
            if ( visited.insert ( transition.second ).second ) {
                q.push ( transition.second );
            } else if ( usefulStates.contains ( transition.second ) ) {
                return true;
            }
        }
    }
 
    return false;
}
 
} /* namespace properties */
 
} /* namespace automaton */