记牢希尔查询

希尔排序：void shellsort3(int a[], int n)  {      int i, j, gap;      for (gap = n / 2; gap > 0; gap /= 2)          for (i = gap; i < n; i++)              for (j = i - gap; j >= 0 && a[j] > a[j + gap]; j -= gap)                  Swap(a[j], a[j + gap]);  }