Combinations.hpp

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#pragma ident "$Id: Combinations.hpp 3140 2012-06-18 15:03:02Z susancummins $"

#ifndef COMBINATIONS_INCLUDE
#define COMBINATIONS_INCLUDE

namespace gpstk {

#include "Exception.hpp"

class Combinations {
public:
   Combinations(void) throw()
   {
      nc = n = k = 0;
      Index = std::vector<int>(0);
   }

   Combinations(int N, int K) throw(Exception)
   { init(N,K); }

   Combinations(const Combinations& right)
      throw()
   {
      *this = right;
   }

   Combinations& operator=(const Combinations& right) throw()
   {
      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) throw() {
      if(k < 1) return -1;
      if(Increment(k-1) != -1) return ++nc;
      return -1;
   }

   int Selection(int j) throw()
   {
      if(j < 0 || j >= k) return -1;
      return Index[j];
   }

   bool isSelected(int j) throw()
   {
      for(int i=0; i<k; i++)
         if(Index[i] == j) return true;
      return false;
   }

private:

   void init(int N, int K) throw(Exception)
   {
      if(K > N || N < 0 || K < 0) {
         Exception e("Combinations(n,k) must have k <= n, with n,k >= 0");
         GPSTK_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) throw()
   {
      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 gpstk

#endif // COMBINATIONS_INCLUDE

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