vcglib/vcg/math/disjoint_set.h

/****************************************************************************
* VCGLib                                                            o o     *
* Visual and Computer Graphics Library                            o     o   *
*                                                                _   O  _   *
* Copyright(C) 2004                                                \/)\/    *
* Visual Computing Lab                                            /\/|      *
* ISTI - Italian National Research Council                           |      *
*                                                                    \      *
* All rights reserved.                                                      *
*                                                                           *
* This program 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 2 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 (http://www.gnu.org/licenses/gpl.txt)          *
* for more details.                                                         *
*                                                                           *
****************************************************************************/

#ifndef VCG_MATH_UNIONSET_H
#define VCG_MATH_UNIONSET_H


// some stuff for portable hashes...
#ifdef WIN32
 #ifndef __MINGW32__
  #include <hash_map>
  #include <hash_set>
  #define STDEXT stdext
 #else
  #include <ext/hash_map>
  #include <ext/hash_set>
  #define STDEXT __gnu_cxx
 #endif
#else
 #include <ext/hash_map>
 #include <ext/hash_set>
 #define STDEXT __gnu_cxx
// It's terrible but gnu's hash_map needs an instantiation of hash() for
// every key type! So we cast the pointer to void*
namespace __gnu_cxx
{
	template <> class hash<void *>: private hash<unsigned long>
	{
	public:
		size_t operator()(const void *ptr) const { return hash<unsigned long>::operator()((unsigned long)ptr); }
	};
}
#endif

#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;
#ifdef __GNUC__
 		typedef typename STDEXT::hash_map< /*ObjectPointer*/void*, int >::iterator	hIterator;
#else
		typedef typename STDEXT::hash_map< ObjectPointer, int >::iterator	hIterator;
#endif
		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:
#ifdef __GNUC__
 		STDEXT::hash_map< void*, int > inserted_objects;
#else
		STDEXT::hash_map< OBJECT_TYPE*, int > inserted_objects;
#endif
		std::vector< DisjointSetNode >				nodes;
	};
};// end of namespace vcg

#endif //VCG_MATH_UNIONSET_H