openMVS/vcglib/vcg/math/disjoint_set.h

/****************************************************************************
* VCGLib                                                            o o     *
* Visual and Computer Graphics Library                            o     o   *
*                                                                _   O  _   *
* Copyright(C) 2004-2016                                           \/)\/    *
* Visual Computing Lab                                            /\/|      *
* ISTI - Italian National Research Council                           |      *
*                                                                    \      *
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* (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 (http://www.gnu.org/licenses/gpl.txt)          *
* for more details.                                                         *
*                                                                           *
****************************************************************************/

#ifndef VCG_MATH_UNIONSET_H
#define VCG_MATH_UNIONSET_H

#include <unordered_map>
#include <vector>
#include <assert.h>

namespace vcg
{
  /*!
  * Given a set of elements, it is often useful to break them up or partition them into a number of separate, nonoverlapping groups.
  * A disjoint-set data structure is a data structure that keeps track of such a partitioning. See
  * <a href="http://en.wikipedia.org/wiki/Disjoint-set_data_structure">Diskoint-set data structure on Wikipedia </a> for more details.
  */
  template<class OBJECT_TYPE>
  class DisjointSet
  {
    /*************************************************
    *		Inner class definitions
    **************************************************/
    struct DisjointSetNode
    {
      DisjointSetNode(OBJECT_TYPE *x) {obj=x; parent=obj; rank=0;}
      OBJECT_TYPE	*obj;
      OBJECT_TYPE *parent;
      int					 rank;
    };

    typedef OBJECT_TYPE*																							ObjectPointer;
    typedef std::pair< ObjectPointer, int >														hPair;

    struct SimpleObjHashFunc{
      inline	size_t	operator ()(const ObjectPointer &p) const {return size_t(p);}
    };

    std::unordered_map< OBJECT_TYPE*, int > inserted_objects;
    typedef typename std::unordered_map< OBJECT_TYPE*, int >::iterator	hIterator;

    typedef std::pair< hIterator, bool >															hInsertResult;


  public:
    /*!
    * Default constructor
    */
    DisjointSet() {}

    /*!
    * Makes a group containing only a given element (a singleton).
    */
    void MakeSet(OBJECT_TYPE *x)
    {
      int object_count		= int(inserted_objects.size());
      assert(inserted_objects.find(x)==inserted_objects.end()); //the map mustn't already contain the object x
      nodes.push_back(DisjointSetNode(x));
      inserted_objects.insert( hPair(x,object_count) );
    }

    /*!
    * Combine or merge two groups into a single group.
    */
    void Union(OBJECT_TYPE *x, OBJECT_TYPE *y)
    {
      OBJECT_TYPE *s0 = FindSet(x);
      OBJECT_TYPE *s1 = FindSet(y);
      Link(s0, s1);
    }

    /*!
    * Determine which group a particular element is in.
    */
    OBJECT_TYPE* FindSet(OBJECT_TYPE *x)
    {
      hIterator pos = inserted_objects.find(x);
      assert(pos!=inserted_objects.end());
      DisjointSetNode *node = &nodes[pos->second];
      if (node->parent!=x)
        node->parent = FindSet(node->parent);
      return node->parent;
    }

  private:
    /*
    */
    void Link(OBJECT_TYPE *x, OBJECT_TYPE *y)
    {
      hIterator xPos = inserted_objects.find(x);
      hIterator yPos = inserted_objects.find(y);
      assert(xPos!=inserted_objects.end() && yPos!=inserted_objects.end());
      DisjointSetNode *xNode = &nodes[xPos->second];
      DisjointSetNode *yNode = &nodes[yPos->second];
      if (xNode->rank>yNode->rank)
        xNode->parent = y;
      else
      {
        yNode->parent = x;
        if (xNode->rank==yNode->rank)
          yNode->rank++;
      }
    }

  protected:
    std::vector< DisjointSetNode >				nodes;
  };
};// end of namespace vcg

#endif //VCG_MATH_UNIONSET_H