最短寻道时间优先（SSTF）和扫描（SCAN）算法。可以对给出的任意的磁盘请求序列、计算平均寻道长度； 要求可定制磁盘请求序列长度、磁头起始位置、磁头移动方向。-Shortest seek time first (SSTF) and scanning (SCAN) algorithm. Can be given any sequence of disk requests, calculate the average seek length requirements can be customi