#if !defined  HAVE_RGS_FINCR_H__
#define       HAVE_RGS_FINCR_H__
// This file is part of the FXT library.
// Copyright (C) 2010 Joerg Arndt
// License: GNU General Public License version 3 or later,
// see the file COPYING.txt in the main directory.

#include "fxttypes.h"


class rgs_fincr
// Restricted growth strings (RGS) s[0,...,n-1] so that
//  s[k] <= F[k]+i  where
//  F[0]=0, F[k+1]=( s[k+1]-s[k]==i ?  F[k]+i : F[k] )
// Lexicographic order
{
public:
    ulong *s_;  // restricted growth string
    ulong *f_;  // values F(k)
    ulong n_;   // Length of strings
    ulong i_;   // s[k] <= f[k]+i
    // i==1 ==> RGS for set partitions

public:
    rgs_fincr(ulong n, ulong i=1)
    {
        n_ = n;
        f_ = new ulong[n_];
        s_ = new ulong[n_];
        i_ = i;
        first();
    }

    ~rgs_fincr()
    {
        delete [] f_;
        delete [] s_;
    }

    void first()
    {
        ulong n = n_;
        for (ulong k=0; k<n; ++k)  s_[k] = 0;
        for (ulong k=0; k<n; ++k)  f_[k] = 0;
    }

    ulong next()
    // Return index of first changed element in s[],
    // Return zero if current string is the last
    {
        ulong k = n_;

    start:
        --k;
        if ( k==0 )  return 0;

        ulong sk = s_[k] + 1;
        ulong m1 = f_[k-1];
        ulong mp = m1 + i_;
        if ( sk > mp )  // "carry"
        {
            s_[k] = 0;
            goto start;
        }

        s_[k] = sk;
        if ( sk==mp )  m1 += i_;
        for (ulong j=k; j<n_; ++j )  f_[j] = m1;

        return k;
    }

    const ulong* data()  const  { return s_; }

    void print(bool nsq=false)  const;
};
// -------------------------


#endif  // !defined HAVE_RGS_FINCR_H__