Compaction.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 <stack>
#include <alib/tuple>
 
#include <automaton/FSM/CompactDFA.h>
#include <automaton/FSM/CompactNFA.h>
#include <automaton/FSM/NFA.h>
#include <automaton/FSM/DFA.h>
 
namespace automaton {
 
namespace transform {
 
class Compaction {
    template < class T >
    using CompactAutomaton = typename std::conditional < isDFA < T >, automaton::CompactDFA < typename T::SymbolType, typename T::StateType >, automaton::CompactNFA < typename T::SymbolType, typename T::StateType > >::type;
 
public:
    template < class T >
    requires isDFA < T > || isNFA < T >
    static Compaction::CompactAutomaton < T > convert ( const T & automaton);
 
    template < class T >
    requires isCompactDFA < T > || isCompactNFA < T >
    static T convert ( const T & automaton );
};
 
template < class T >
requires isCompactDFA < T > || isCompactNFA < T >
T Compaction::convert ( const T & automaton ) {
    return automaton;
}
 
template < class T >
requires isDFA < T > || isNFA < T >
Compaction::CompactAutomaton < T > Compaction::convert ( const T & automaton) {
    using SymbolType = typename T::SymbolType;
    using StateType = typename T::StateType;
 
    CompactAutomaton < T > res(automaton.getInitialState());
    res.setInputAlphabet(automaton.getInputAlphabet());
 
    ext::set < ext::tuple < StateType, StateType, SymbolType > > visited;
 
    std::stack<ext::tuple<StateType, StateType, SymbolType>> stack; // state x lastFork x symbol we used to go to that state
    for(const auto& transition: automaton.getTransitionsFromState(automaton.getInitialState()))
        stack.push(ext::make_tuple(transition.second, automaton.getInitialState(), transition.first.second));
 
    if(automaton.getFinalStates().count(automaton.getInitialState()))
        res.addFinalState(automaton.getInitialState());
 
    while(!stack.empty()) {
        StateType q = std::move(std::get<0>(stack.top()));
        StateType lastFork = std::move(std::get<1>(stack.top()));
        SymbolType symbol = std::move(std::get<2>(stack.top()));
        stack.pop();
 
        ext::vector < SymbolType > path { std::move ( symbol ) };
 
        decltype ( automaton.getTransitionsFromState ( q ) ) transitions;
        // only 1 child and nonfinal
        while((transitions = automaton.getTransitionsFromState(q)).size() == 1 && automaton.getFinalStates().count(q) == 0) {
            const std::pair<ext::pair<StateType, SymbolType>, StateType>& transition = * transitions.begin();
            path.push_back(transition.first.second);
            q = transition.second;
        }
 
        for(const std::pair<const ext::pair<StateType, SymbolType>, StateType>& transition : transitions )
            if(visited.insert(ext::make_tuple(transition.second, q, transition.first.second)).second)
                stack.push(ext::make_tuple(transition.second, q, transition.first.second));
 
        // fork or final state
        res.addState(q);
 
        if(automaton.getFinalStates().count(q))
            res.addFinalState(q);
 
        res.addTransition ( std::move ( lastFork ), std::move ( path ), std::move ( q ) );
 
    }
 
    return res;
}
 
} /* namespace transform */
 
} /* namespace automaton */