修改起泡排序的算法，在正反两个方向交替进行扫描，即第一趟把排序码最大的对象放到序列的最后，第二趟把排序码最小的对象放到序列的最前面。如此反复进行。-Modified bubble sort algorithm, in both directions alternately scanning, sorting code that first trip to the largest objects into the final, the second trip to the smallest obj