Question

这是我已经实施的：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <dirent.h>
#include <libgen.h>

/* checks if the string is purely an integer
 * we can do it with `strtol' also
 */
int check_if_number (char *str)
{
  int i;
  for (i=0; str[i] != '\0'; i++)
  {
    if (!isdigit (str[i]))
    {
      return 0;
    }
  }
  return 1;
}

#define MAX_BUF 1024
#define PID_LIST_BLOCK 32

int *pidof (char *pname)
{
  DIR *dirp;
  FILE *fp;
  struct dirent *entry;
  int *pidlist, pidlist_index = 0, pidlist_realloc_count = 1;
  char path[MAX_BUF], read_buf[MAX_BUF];

  dirp = opendir ("/proc/");
  if (dirp == NULL)
  {
    perror ("Fail");
    return NULL;
  }

  pidlist = malloc (sizeof (int) * PID_LIST_BLOCK);
  if (pidlist == NULL)
  {
    return NULL;
  }

  while ((entry = readdir (dirp)) != NULL)
  {
    if (check_if_number (entry->d_name))
    {
      strcpy (path, "/proc/");
      strcat (path, entry->d_name);
      strcat (path, "/comm");

      /* A file may not exist, it may have been removed.
       * dut to termination of the process. Actually we need to
       * make sure the error is actually file does not exist to
       * be accurate.
       */
      fp = fopen (path, "r");
      if (fp != NULL)
      {
        fscanf (fp, "%s", read_buf);
        if (strcmp (read_buf, pname) == 0)
        {
          /* add to list and expand list if needed */
          pidlist[pidlist_index++] = atoi (entry->d_name);
          if (pidlist_index == PID_LIST_BLOCK * pidlist_realloc_count)
          {
            pidlist_realloc_count++;
            pidlist = realloc (pidlist, sizeof (int) * PID_LIST_BLOCK * pidlist_realloc_count); //Error check todo
            if (pidlist == NULL)
            {
              return NULL;
            }
          }
        }
        fclose (fp);
      }
    }
  }


  closedir (dirp);
  pidlist[pidlist_index] = -1; /* indicates end of list */
  return pidlist;
}

int main (int argc, char *argv[])
{
  int *list, i;

  if (argc != 2)
  {
    printf ("Usage: %s proc_name\n", argv[0]);
    return 0;
  }
  list = pidof (argv[1]);
  for (i=0; list[i] != -1; i++)
  {
    printf ("%d ", list[i]);
  }
  free (list);
  if (list[0] != -1)
  {
    printf ("\n");
  }
  return 0;
}

当n = 3时，我得到了：

function B = bell(n)
B(1,1) = 1;
for i=2:n
    B(i,1) = B(1,end);
    for j = 1:i-1
        B(i-j,j+1) = B(i-1,j)+B(i,j);
    end
end
end

而不是：

 1     2     3
 1     3     0
 2     0     0

Answer 1

您需要更改行

B(i-j,j+1) = B(i-1,j)+B(i,j);

到

B(i-j,j+1) = B(i-j+1,j)+B(i-j,j);

示例：for n=5，

B =
     1     2     5    15    52
     1     3    10    37     0
     2     7    27     0     0
     5    20     0     0     0
    15     0     0     0     0

根据this。

在Matlab中计算Bell数

1 个答案: