/* glpapi18.c (maximum clique problem) */

/***********************************************************************

*  This code is part of GLPK (GNU Linear Programming Kit).

*

*  Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008,

*  2009, 2010 Andrew Makhorin, Department for Applied Informatics,

*  Moscow Aviation Institute, Moscow, Russia. All rights reserved.

*  E-mail: <mao@gnu.org>.

*

*  GLPK 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 3 of the License, or

*  (at your option) any later version.

*

*  GLPK 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 GLPK. If not, see <http://www.gnu.org/licenses/>.

***********************************************************************/

#include "glpapi.h"

#include "glpnet.h"

static void set_edge(int nv, unsigned char a[], int i, int j)

{     int k;

      xassert(1 <= j && j < i && i <= nv);

      k = ((i - 1) * (i - 2)) / 2 + (j - 1);

      a[k / CHAR_BIT] |=

         (unsigned char)(1 << ((CHAR_BIT - 1) - k % CHAR_BIT));

      return;

}

int glp_wclique_exact(glp_graph *G, int v_wgt, double *sol, int v_set)

{     /* find maximum weight clique with exact algorithm */

      glp_arc *e;

      int i, j, k, len, x, *w, *ind, ret = 0;

      unsigned char *a;

      double s, t;

      if (v_wgt >= 0 && v_wgt > G->v_size - (int)sizeof(double))

         xerror("glp_wclique_exact: v_wgt = %d; invalid parameter\n",

            v_wgt);

      if (v_set >= 0 && v_set > G->v_size - (int)sizeof(int))

         xerror("glp_wclique_exact: v_set = %d; invalid parameter\n",

            v_set);

      if (G->nv == 0)

      {  /* empty graph has only empty clique */

         if (sol != NULL) *sol = 0.0;

         return 0;

      }

      /* allocate working arrays */

      w = xcalloc(1+G->nv, sizeof(int));

      ind = xcalloc(1+G->nv, sizeof(int));

      len = G->nv; /* # vertices */

      len = len * (len - 1) / 2; /* # entries in lower triangle */

      len = (len + (CHAR_BIT - 1)) / CHAR_BIT; /* # bytes needed */

      a = xcalloc(len, sizeof(char));

      memset(a, 0, len * sizeof(char));

      /* determine vertex weights */

      s = 0.0;

      for (i = 1; i <= G->nv; i++)

      {  if (v_wgt >= 0)

         {  memcpy(&t, (char *)G->v[i]->data + v_wgt, sizeof(double));

            if (!(0.0 <= t && t <= (double)INT_MAX && t == floor(t)))

            {  ret = GLP_EDATA;

               goto done;

            }

            w[i] = (int)t;

         }

         else

            w[i] = 1;

         s += (double)w[i];

      }

      if (s > (double)INT_MAX)

      {  ret = GLP_EDATA;

         goto done;

      }

      /* build the adjacency matrix */

      for (i = 1; i <= G->nv; i++)

      {  for (e = G->v[i]->in; e != NULL; e = e->h_next)

         {  j = e->tail->i;

            /* there exists edge (j,i) in the graph */

            if (i > j) set_edge(G->nv, a, i, j);

         }

         for (e = G->v[i]->out; e != NULL; e = e->t_next)

         {  j = e->head->i;

            /* there exists edge (i,j) in the graph */

            if (i > j) set_edge(G->nv, a, i, j);

         }

      }

      /* find maximum weight clique in the graph */

      len = wclique(G->nv, w, a, ind);

      /* compute the clique weight */

      s = 0.0;

      for (k = 1; k <= len; k++)

      {  i = ind[k];

         xassert(1 <= i && i <= G->nv);

         s += (double)w[i];

      }

      if (sol != NULL) *sol = s;

      /* mark vertices included in the clique */

      if (v_set >= 0)

      {  x = 0;

         for (i = 1; i <= G->nv; i++)

            memcpy((char *)G->v[i]->data + v_set, &x, sizeof(int));

         x = 1;

         for (k = 1; k <= len; k++)

         {  i = ind[k];

            memcpy((char *)G->v[i]->data + v_set, &x, sizeof(int));

         }

      }

done: /* free working arrays */

      xfree(w);

      xfree(ind);

      xfree(a);

      return ret;

}

/* eof */