tsp.c

掌握如何用C来实现各种算法

/*****************************************************************************
*                                                                            *
*  --------------------------------- tsp.c --------------------------------  *
*                                                                            *
*****************************************************************************/

#include <float.h>
#include <math.h>
#include <stdlib.h>

#include "graph.h"
#include "graphalg.h"
#include "list.h"

/*****************************************************************************
*                                                                            *
*  ---------------------------------- tsp ---------------------------------  *
*                                                                            *
*****************************************************************************/

int tsp(List *vertices, const TspVertex *start, List *tour, int (*match)
   (const void *key1, const void *key2)) {

TspVertex          *tsp_vertex,
                   *tsp_start,
                   *selection;

ListElmt           *element;

double             minimum,
                   distance,
                   x,
                   y;

int                found,
                   i;

/*****************************************************************************
*                                                                            *
*  Initialize the list for the tour.                                         *
*                                                                            *
*****************************************************************************/

list_init(tour, NULL);

/*****************************************************************************
*                                                                            *
*  Initialize all of the vertices in the graph.                              *
*                                                                            *
*****************************************************************************/

found = 0;

for (element = list_head(vertices); element != NULL; element =
   list_next(element)) {

   tsp_vertex = list_data(element);

   if (match(tsp_vertex, start)) {

      /***********************************************************************
      *                                                                      *
      *  Start the tour at the start vertex.                                 *
      *                                                                      *
      ***********************************************************************/

      if (list_ins_next(tour, list_tail(tour), tsp_vertex) != 0) {

         list_destroy(tour);
         return -1;

      }

      /***********************************************************************
      *                                                                      *
      *  Save the start vertex and its coordinates.                          *
      *                                                                      *
      ***********************************************************************/

      tsp_start = tsp_vertex;
      x = tsp_vertex->x;
      y = tsp_vertex->y;

      /***********************************************************************
      *                                                                      *
      *  Color the start vertex black.                                       *
      *                                                                      *
      ***********************************************************************/

      tsp_vertex->color = black;
      found = 1;

      }

   else {

      /***********************************************************************
      *                                                                      *
      *  Color all other vertices white.                                     *
      *                                                                      *
      ***********************************************************************/

      tsp_vertex->color = white;

   }

}

/*****************************************************************************
*                                                                            *
*  Return if the start vertex was not found.                                 *
*                                                                            *
*****************************************************************************/

if (!found) {

   list_destroy(tour);
   return -1;

}

/*****************************************************************************
*                                                                            *
*  Use the nearest-neighbor heuristic to compute the tour.                   *
*                                                                            *
*****************************************************************************/

i = 0;

while (i < list_size(vertices) - 1) {

   /**************************************************************************
   *                                                                         *
   *  Select the white vertex closest to the previous vertex in the tour.    *
   *                                                                         *
   **************************************************************************/

   minimum = DBL_MAX;

   for (element = list_head(vertices); element != NULL; element =
      list_next(element)) {

      tsp_vertex = list_data(element);

      if (tsp_vertex->color == white) {

         distance = sqrt(pow(tsp_vertex->x-x,2.0) + pow(tsp_vertex->y-y,2.0));

         if (distance < minimum) {

            minimum = distance;
            selection = tsp_vertex;

         }

      }

   }

   /**************************************************************************
   *                                                                         *
   *  Save the coordinates of the selected vertex.                           *
   *                                                                         *
   **************************************************************************/

   x = selection->x;
   y = selection->y;

   /**************************************************************************
   *                                                                         *
   *  Color the selected vertex black.                                       *
   *                                                                         *
   **************************************************************************/

   selection->color = black;

   /**************************************************************************
   *                                                                         *
   *  Insert the selected vertex into the tour.                              *
   *                                                                         *
   **************************************************************************/

   if (list_ins_next(tour, list_tail(tour), selection) != 0) {

      list_destroy(tour);
      return -1;

   }

   /**************************************************************************
   *                                                                         *
   *  Prepare to select the next vertex.                                     *
   *                                                                         *
   **************************************************************************/

   i++;

}

/*****************************************************************************
*                                                                            *
*  Insert the start vertex again to complete the tour.                       *
*                                                                            *
*****************************************************************************/

if (list_ins_next(tour, list_tail(tour), tsp_start) != 0) {

   list_destroy(tour);
   return -1;

}

return 0;

}