Always move the disk arm in one direction (opposite to 0), after processing the highest numbered track, move to the lowest numbered track with read-write request, and then continue to move up.

Here, you can understand it in reverse, that is, from high to low.

Visit 168 first, then visit 140, 1 17. There are no requests for tracks smaller than 1 17. At this time, the disc arm should return to 288, and then move in the direction of 0.