sides_to_elem_map.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2025 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner

// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.

// This library 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
// Lesser General Public License for more details.

// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

#ifndef LIBMESH_SIDES_TO_ELEM_MAP_H
#define LIBMESH_SIDES_TO_ELEM_MAP_H

// libMesh includes
#include "libmesh/id_types.h" // dof_id_type
#include "libmesh/hashword.h" // Utility::hashword()

// C++ includes
#include <unordered_map>
#include <vector>

namespace libMesh
{

// Forward declarations
class MeshBase;
class Elem;

namespace MeshTools
{

class SidesToElemMap
{
public:
  SidesToElemMap();
  ~SidesToElemMap();

  static SidesToElemMap build(const MeshBase & mesh);

  typedef std::vector<const Elem *>::const_iterator ElemIter;

  std::pair<ElemIter, ElemIter>
  get_connected_elems(const Elem * elem, unsigned int side) const;

private:

  typedef std::vector<dof_id_type> Key;
  typedef std::vector<const Elem *> Value;

  struct HashFunction
  {
  public:
    inline
    std::size_t operator()(const Key & vertex_ids) const
    {
      return cast_int<std::size_t>(Utility::hashword(vertex_ids));
    }

    inline
    bool operator()(const Key & lhs, const Key & rhs) const
    {
      return lhs == rhs;
    }
  };

  std::unordered_map<Key, Value, /*Hash*/HashFunction, /*KeyEqual*/HashFunction> _sides_to_elem_map;

  void get_sorted_vertex_ids(
    const Elem * elem,
    unsigned int side,
    std::vector<dof_id_type> & sorted_vertex_ids) const;
};

} // namespace MeshTools

} // namespace libMesh

#endif // LIBMESH_SIDES_TO_ELEM_MAP_H