JCombinatorics.hh

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#ifndef __JTOOLS__JCOMBINATORICS__
#define __JTOOLS__JCOMBINATORICS__

#include <utility>
#include <vector>
#include <algorithm>


/**
 * \author mdejong
 */

namespace JTOOLS {}
namespace JPP { using namespace JTOOLS; }

namespace JTOOLS {


  /**
   * Auxiliary class to convert pair of indices to unique index and back.
   */
  class JCombinatorics {
  public:
    /**
     * Data structure for a pair of indices.
     */
    struct pair_type :
      public std::pair<int, int>  
    {
      /**
       * Default constructor.
       */
      pair_type() :
        std::pair<int, int>(-1, -1)
      {}


      /**
       * Constructor.
       *
       * \param  first                 first  index
       * \param  second                second index
       */
      pair_type(const int first, const int second) :
        std::pair<int, int>(first, second)
      {}
    

      /**
       * Less-than operator.
       *
       * \param  first                 first  pair
       * \param  second                second pair
       * \return                       true if first pair less than second; else false
       */
      friend inline bool operator<(const pair_type& first, const pair_type& second)
      {
        if (first.first == second.first)
          return first.second < second.second;
        else
          return first.first  < second.first;
      }
    };


    /**
     * Default constructor.
     */
    JCombinatorics() 
    {}


    /**
     * Constructor.
     *
     * \param  numberOfIndices       number of indices
     */
    JCombinatorics(const int numberOfIndices) 
    {
      configure(numberOfIndices);
    }


    /**
     * Get combinatorics.
     *
     * \return                       combinatorics
     */
    const JCombinatorics& getCombinatorics() const
    {
      return *this;
    }


    /**
     * Configure.
     *
     * \param  numberOfIndices       number of indices
     */
    void configure(const int numberOfIndices) 
    {
      zbuf1D.clear();

      zbuf2D.resize(numberOfIndices);

      for (int i = 0; i != numberOfIndices; ++i) {
        zbuf2D[i].resize(numberOfIndices);
      }

      for (int i = 0; i != numberOfIndices; ++i) {

        zbuf2D[i][i] = -1;

        for (int j = i; ++j != numberOfIndices; ) {

          zbuf2D[i][j] = zbuf1D.size();
          zbuf2D[j][i] = zbuf1D.size();

          zbuf1D.push_back(pair_type(i,j));
        }
      }
    }


    /**
     * Get number of indices.
     *
     * \return                       number of indices
     */
    size_t getNumberOfIndices() const
    {
      return zbuf2D.size();
    }


    /**
     * Get number of pairs.
     *
     * \return                       number of pairs
     */
    size_t getNumberOfPairs() const
    {
      return zbuf1D.size();
    }
  
  
    /**
     * Get index of pair of indices.
     *
     * \param  first                 first  address
     * \param  second                second address
     * \return                       index (-1 if first and second address are equal)
     */
    int getIndex(const int first, const int second) const
    {
      return zbuf2D[first][second];
    }
  
  
    /**
     * Get index of pair.
     *
     * \param  pair                  pair
     * \return                       index (-1 if first and second address are equal)
     */
    int getIndex(const pair_type& pair) const
    {
      return getIndex(pair.first, pair.second);
    }


    /**
     * Get pair of indices for given index.
     *
     * \param  index                 index
     * \return                       pair of indices
     */
    const pair_type& getPair(const int index) const
    {
      return zbuf1D[index];
    }


    /**
     * Sort address pairs.
     *
     * \param  comparator            comparator for pairs
     */
    template<class JComparator_t>
    void sort(JComparator_t comparator)
    {
      std::stable_sort(zbuf1D.begin(), zbuf1D.end(), comparator);

      for (int i = 0; i != (int) zbuf1D.size(); ++i) {
        
        const pair_type pair = zbuf1D[i];

        zbuf2D[pair.first][pair.second] = i;
        zbuf2D[pair.second][pair.first] = i;
      }

      for (int i = 0; i != (int) zbuf2D.size(); ++i) {
        zbuf2D[i][i] = -1;
      }
    }


    /**
     * Sign of pair of indices.
     *
     * \param  first                 first  address
     * \param  second                second address
     * \return                       +1 if second >= first; else -1
     */
    static int getSign(const int first, const int second)
    {
      return (second >= first ? +1 : -1);
    }


    /**
     * Sign of pair of indices.
     *
     * \param  pair                  pair of indices
     * \return                       +1 if second >= first; else -1
     */
    static int getSign(const pair_type& pair)
    {
      return getSign(pair.first, pair.second);
    }


  protected:
    std::vector<pair_type>         zbuf1D;
    std::vector<std::vector<int> > zbuf2D;
  };
}

#endif