int reduce(int *a, int n)
{
        int i, j, dup;

        if (!a || n < 0)
                return -1;

        i = dup = 0;

        while (i < (n - dup - 1)) {
                if (a[i] == a[i+1]) {
                        dup++;
                        for (j = i ; j < (n - dup); j++)
                                a[j] = a[j+1];
                } else
                        i++;
        }

        return n - dup;
}