accessible.hh

Go to the documentation of this file.

// This file is part of Awali.
// Copyright 2016-2022 Sylvain Lombardy, Victor Marsault, Jacques Sakarovitch
//
// Awali is a 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.
//
// This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
 
/* @file accessible.hh
 *
 * This files contains static functions computing accessible states.
 */
#ifndef AWALI_ALGOS_ACCESSIBLE_HH
#define AWALI_ALGOS_ACCESSIBLE_HH
 
#include <deque>
#include <queue>
#include <map>
#include <unordered_set>
 
#include <awali/sttc/algos/copy.hh>
#include <awali/sttc/algos/sub_automaton.hh>
#include <awali/sttc/core/transpose_view.hh>
#include <awali/sttc/misc/attributes.hh>
#include <awali/sttc/misc/set.hh>
 
namespace awali {
  namespace sttc {
 
 
  /*--------------------------------------------------.
  | Sets of accessible, coaccessible, useful states.  |
  `--------------------------------------------------*/
 
  // The set of accessible states, including pre(), and possibly post().
  //breadth first search
    template <typename Set, typename Aut>
    void
    fill_with_accessible_states(Set& res, const Aut& aut, bool include_pre_post=false) {
      // Reachable states.
      const auto& a = *aut;
      if(include_pre_post)
        res.emplace(a.pre());
      
      // States work list.
      using worklist_t = std::queue<state_t>;
      worklist_t todo;
      todo.emplace(a.pre());
      
      while (!todo.empty())
        {
          const state_t src = todo.front();
          todo.pop();
          
          for (auto tr : a.all_out(src))
            {
              state_t dst = a.dst_of(tr);
              // If we have not seen it already, explore its successors.
              if(dst != a.post() || include_pre_post)
                if (res.emplace(dst).second)
                  todo.emplace(dst);
            }
        }
    }
    
    template <typename Aut>
    std::set<state_t>
    accessible_states(const Aut& aut, bool include_pre_post=false)
    {
      // Reachable states.
      std::set<state_t> res;
      fill_with_accessible_states(res, aut, include_pre_post);
      return res;
    }
 
    template <typename Set, typename Aut>
    void
    fill_with_coaccessible_states(Set& res, const Aut& aut, bool include_pre_post=false) {
      fill_with_accessible_states(res, transpose_view(aut), false);
    }
    
    // The set of coaccessible states, including post(), and possibly pre().
    template <typename Aut>
    std::set<state_t>
    coaccessible_states(const Aut& aut, bool include_pre_post=false)
    {
      return accessible_states(transpose_view(aut), false);
    }
 
    // The set of coaccessible states, including post(), and possibly pre().
    template <typename Aut>
    std::set<state_t>
    useful_states(const Aut& aut, bool include_pre_post=false)
    {
      auto accessible = accessible_states(aut, false);
      auto coaccessible = coaccessible_states(aut, false);
      return internal::intersection(accessible, coaccessible);
    }
 
 
    /*----------------------------------------------------.
      | Number of accessible, coaccessible, useful states.  |
      `----------------------------------------------------*/
 
    template <typename Aut>
    size_t
    num_accessible_states(const Aut& aut)
    {
      std::unordered_set<state_t> set;
      fill_with_accessible_states(set,aut);
      return set.size();
    }
 
    template <typename Aut>
    size_t
    num_coaccessible_states(const Aut& aut)
    {
      std::unordered_set<state_t> set;
      fill_with_coaccessible_states(set,aut);
      return set.size();
    }
 
    template <typename Aut>
    size_t
    num_useful_states(const Aut& aut)
    {
      auto set = useful_states(aut);
      return set.size();
    }
 
 
    /*-----------------------------------------------.
      | accessible, coaccessible, useful subautomata.  |
      `-----------------------------------------------*/
 
    template <typename Aut>
    typename Aut::element_type::automaton_nocv_t
    accessible(const Aut& aut, bool keep_history=true)
    {
      return copy(aut, accessible_states(aut), keep_history);
    }
    
    template <typename Aut>
    void
    accessible_here(Aut& aut)
    {
      return sub_automaton(aut, accessible_states(aut));
    }
 
    template <typename Aut>
    typename Aut::element_type::automaton_nocv_t
    coaccessible(const Aut& aut, bool keep_history=true)
    {
      return copy(aut, coaccessible_states(aut), keep_history);
    }
 
    template <typename Aut>
    void
    coaccessible_here(Aut& aut)
    {
      return sub_automaton(aut, coaccessible_states(aut));
    }
 
    template <typename Aut>
    typename Aut::element_type::automaton_nocv_t
    trim(const Aut& aut, bool keep_history=true)
    {
      return copy(aut, useful_states(aut), keep_history);
    }
 
    template <typename Aut>
    void
    trim_here(Aut& aut)
    {
      return sub_automaton(aut, useful_states(aut));
    }
    
    /*----------------------------------------------------------------.
      | is_trim, is_accessible, is_coaccessible, is_empty, is_useless.  |
      `----------------------------------------------------------------*/
 
    template <typename Aut>
    bool is_trim(const Aut& aut)
    {
      return num_useful_states(aut) == aut->num_states();
    }
 
    template <typename Aut>
    bool is_useless(const Aut& aut)
    {
      return num_useful_states(aut) == 0;
    }
 
    template <typename Aut>
    bool is_accessible(const Aut& aut)
    {
      return num_accessible_states(aut) == aut->num_states();
    }
 
    template <typename Aut>
    bool is_coaccessible(const Aut& aut)
    {
      return num_coaccessible_states(aut) == aut->num_states();
    }
 
    template <typename Aut>
    bool is_empty(const Aut& aut) ATTRIBUTE_PURE;
 
    template <typename Aut>
    bool is_empty(const Aut& aut)
    {
      return aut->num_states() == 0;
    }
 
  }
}//end of ns awali::stc
 
#endif // !AWALI_ALGOS_ACCESSIBLE_HH