/* combination/combination.c
 * based on permutation/permutation.c by Brian Gough
 * 
 * Copyright (C) 2001 Szymon Jaroszewicz
 * 
 * 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 for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <config.h>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_combination.h>

extern int gsl_check_range ; /* defined in vector/vector.c */

size_t
gsl_combination_n (const gsl_combination * c)
{
  return c->n ;
}

size_t
gsl_combination_k (const gsl_combination * c)
{
  return c->k ;
}

size_t *
gsl_combination_data (const gsl_combination * c)
{
  return c->data ;
}

#ifndef HIDE_INLINE_STATIC
size_t
gsl_combination_get (const gsl_combination * c, const size_t i)
{
  if (gsl_check_range)
    {
      if (i >= c->k)		/* size_t is unsigned, can't be negative */
	{
	  GSL_ERROR_VAL ("index out of range", GSL_EINVAL, 0);
	}
    }

  return c->data[i];
}
#endif


int
gsl_combination_valid (gsl_combination * c)
{
  const size_t n = c->n ;
  const size_t k = c->k ;

  size_t i, j ;

  if( k > n )
    {
      GSL_ERROR("combination has k greater than n", GSL_FAILURE) ;
    }
  for (i = 0; i < k; i++) 
    {
      if (c->data[i] >= n)
        {
          GSL_ERROR("combination index outside range", GSL_FAILURE) ;
        }

      for (j = 0; j < i; j++)
        {
          if (c->data[i] == c->data[j])
            {
              GSL_ERROR("duplicate combination index", GSL_FAILURE) ;
            }
          if (c->data[i] > c->data[j])
            {
              GSL_ERROR("combination index no in increasing order",
			GSL_FAILURE) ;
            }
        }
    }
  
  return GSL_SUCCESS;
}


int
gsl_combination_next (gsl_combination * c)
{
  /* Replaces c with the next combination (in the standard lexicographical
   * ordering).  Returns GSL_FAILURE if there is no next combination.
   */
  const size_t n = c->n;
  const size_t k = c->k;
  size_t *data = c->data;
  size_t i;

  if(k == 0)
    {
      return GSL_FAILURE;
    }
  i = k - 1;

  while(i > 0 && data[i] == n - k + i)
    {
      i--;
    }
  if(i == 0 && data[i] == n - k)
    {
      return GSL_FAILURE;
    }
  data[i]++;
  for(; i < k - 1; i++)
    {
      data[i + 1] = data[i] + 1;
    }
  return GSL_SUCCESS;
}

int
gsl_combination_prev (gsl_combination * c)
{
  /* Replaces c with the previous combination (in the standard
   * lexicographical ordering).  Returns GSL_FAILURE if there is no
   * previous combination.
   */
  const size_t n = c->n;
  const size_t k = c->k;
  size_t *data = c->data;
  size_t i;

  if(k == 0)
    {
      return GSL_FAILURE;
    }
  i = k - 1;

  while(i > 0 && data[i] == data[i-1] + 1)
    {
      i--;
    }
  if(i == 0 && data[i] == 0)
    {
      return GSL_FAILURE;
    }
  data[i++]--;
  for(; i < k; i++)
    {
      data[i] = n - k + i;
    }
  return GSL_SUCCESS;
}