Combinations.hpp

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//==============================================================================
//
//  This file is part of GNSSTk, the ARL:UT GNSS Toolkit.
//
//  The GNSSTk 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 3.0 of the License, or
//  any later version.
//
//  The GNSSTk 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 GNSSTk; if not, write to the Free Software Foundation,
//  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110, USA
//
//  This software was developed by Applied Research Laboratories at the
//  University of Texas at Austin.
//  Copyright 2004-2022, The Board of Regents of The University of Texas System
//
//==============================================================================
 
//==============================================================================
//
//  This software was developed by Applied Research Laboratories at the
//  University of Texas at Austin, under contract to an agency or agencies
//  within the U.S. Department of Defense. The U.S. Government retains all
//  rights to use, duplicate, distribute, disclose, or release this software.
//
//  Pursuant to DoD Directive 523024
//
//  DISTRIBUTION STATEMENT A: This software has been approved for public
//                            release, distribution is unlimited.
//
//==============================================================================
 
#ifndef COMBINATIONS_INCLUDE
#define COMBINATIONS_INCLUDE
 
#include "Exception.hpp"
 
namespace gnsstk {
 
 
class Combinations {
public:
   Combinations(void) noexcept
   {
      nc = n = k = 0;
      Index = std::vector<int>(0);
   }
 
   Combinations(int N, int K)
   { init(N,K); }
 
   Combinations(const Combinations& right)
      noexcept
   {
      *this = right;
   }
 
   Combinations& operator=(const Combinations& right) noexcept
   {
      init(right.n,right.k);
      nc = right.nc;
      for(int j=0; j<k; j++) Index[j] = right.Index[j];
      return *this;
   }
 
   int Next(void) noexcept {
      if(k < 1) return -1;
      if(Increment(k-1) != -1) return ++nc;
      return -1;
   }
 
   int Selection(int j) noexcept
   {
      if(j < 0 || j >= k) return -1;
      return Index[j];
   }
 
   bool isSelected(int j) noexcept
   {
      for(int i=0; i<k; i++)
         if(Index[i] == j) return true;
      return false;
   }
 
private:
 
   void init(int N, int K)
   {
      if(K > N || N < 0 || K < 0) {
         Exception e("Combinations(n,k) must have k <= n, with n,k >= 0");
         GNSSTK_THROW(e);
      }
 
      Index = std::vector<int>(K);
      nc = 0;
      k = K;
      n = N;
      for(int j=0; j<k; j++)
         Index[j] = j;
   }
 
   int Increment(int j) noexcept
   {
      if(Index[j] < n-k+j) {        // can this index be incremented?
         Index[j]++;
         for(int m=j+1; m<k; m++)
            Index[m]=Index[m-1]+1;
         return 0;
      }
         // is this the last index?
      if(j-1 < 0) return -1;
         // increment the next lower index
      return Increment(j-1);
   }
 
 
   int nc;                  
   int k,n;                 
   std::vector<int> Index;  
 
}; // end class Combinations
 
} // end namespace gnsstk
 
#endif // COMBINATIONS_INCLUDE