ctsort.c

掌握如何用C来实现各种算法

/*****************************************************************************
*                                                                            *
*  ------------------------------- ctsort.c -------------------------------  *
*                                                                            *
*****************************************************************************/

#include <stdlib.h>
#include <string.h>

#include "sort.h"

/*****************************************************************************
*                                                                            *
*  -------------------------------- ctsort --------------------------------  *
*                                                                            *
*****************************************************************************/

int ctsort(int *data, int size, int k) {

int                *counts,
                   *temp;

int                i,
                   j;

/*****************************************************************************
*                                                                            *
*  Allocate storage for the counts.                                          *
*                                                                            *
*****************************************************************************/

if ((counts = (int *)malloc(k * sizeof(int))) == NULL)
   return -1;

/*****************************************************************************
*                                                                            *
*  Allocate storage for the sorted elements.                                 *
*                                                                            *
*****************************************************************************/

if ((temp = (int *)malloc(size * sizeof(int))) == NULL)
   return -1;

/*****************************************************************************
*                                                                            *
*  Initialize the counts.                                                    *
*                                                                            *
*****************************************************************************/

for (i = 0; i < k; i++)
   counts[i] = 0;

/*****************************************************************************
*                                                                            *
*  Count the occurrences of each element.                                    *
*                                                                            *
*****************************************************************************/

for (j = 0; j < size; j++)
   counts[data[j]] = counts[data[j]] + 1;

/*****************************************************************************
*                                                                            *
*  Adjust each count to reflect the counts before it.                        *
*                                                                            *
*****************************************************************************/

for (i = 1; i < k; i++)
   counts[i] = counts[i] + counts[i - 1];

/*****************************************************************************
*                                                                            *
*  Use the counts to position each element where it belongs.                 *
*                                                                            *
*****************************************************************************/

for (j = size - 1; j >= 0; j--) {

   temp[counts[data[j]] - 1] = data[j];
   counts[data[j]] = counts[data[j]] - 1;

}

/*****************************************************************************
*                                                                            *
*  Prepare to pass back the sorted data.                                     *
*                                                                            *
*****************************************************************************/

memcpy(data, temp, size * sizeof(int));

/*****************************************************************************
*                                                                            *
*  Free the storage allocated for sorting.                                   *
*                                                                            *
*****************************************************************************/

free(counts);
free(temp);

return 0;

}