mergesotr.c

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

static void
dump_intv (int *intv,
           int  count)
{
    int i;
    for (i = 0; i < count; i++) {
        printf("%d ", intv[i]);
    }
}

static void
swap (int *a,
      int *b)
{
    int tmp = *a;
    *a = *b;
    *b = tmp;
}

static void
mergesort (int *intv,
           int  count)
{
    if (count == 2) {
        if (intv[0] > intv[1])
            swap (&intv[0], &intv[1]);
    } else if (count > 2) {
        int halfcount, ibm;
        int ia, ib;
        int *a, *b;
        int *tmp;

        halfcount = count / 2;

        tmp = malloc (sizeof (int) * count);
        memcpy (tmp, intv, sizeof (int) * count);

        a = &tmp[0];
        b = &tmp[halfcount];

        ibm = halfcount;
        if (count % 2)
            ++ibm;

        mergesort (a, halfcount);
        mergesort (b, ibm);

        ia = ib = 0;
        while (ia < halfcount && ib < ibm) {
            if (*a < *b)
                intv[(ia++)+ib] = *a++;
            else
                intv[ia+(ib++)] = *b++;
        }

        while (ia < halfcount)
            intv[(ia++)+ib] = *a++;

        while (ib < ibm)
            intv[ia+(ib++)] = *b++;

        free (tmp);
    }
}

int
main (int    argc,
      char **argv)
{
    int i;
    int *numbers;

    argc --;
    argv ++;

    numbers = malloc (sizeof (int) * argc);

    for (i = 0; i < argc; i++) {
        numbers[i] = atoi(argv[i]);
    }

    mergesort (numbers, argc);
    dump_intv (numbers, argc);
    printf ("\n");

    return 0;
}