Train
描述

某列车调度站的铁道联接结构如图所示。

其中，A为入口，B为出口，S为中转盲端。所有铁道均为单轨单向式：列车行驶的方向只能是从A到S，再从S到B；也可以不在S中驻留，直接从A驶向B；另外，不允许超车。因为车厢可在S中驻留，所以它们从B端驶出的次序，可能与从A端驶入的次序不同。不过S的容量有限，同时驻留的车厢不得超过m节。
设某列车由编号依次为{a1, a2, ..., an}的n节车厢组成。调度员希望知道，按照以上交通规则，这些车厢能否以{1, 2, ..., n}的次序，重新排列后从B端驶出。(THU2017 2-1 Train

describe


The railway connection structure of a train dispatching station is shown in the diagram.


Among them, A is the entrance, B is the exit, and S is the blind end of the transfer. All tracks are monorail one-way: the direction of the train is only from A to S, and then from S to B; also can not stay in the S, directly from A to B; in addition, not allowed overtaking. Because the carriage can reside in the S, the order that they exit from the B end may be different from the order from the A end. However, the capacity of S is limited, and the carriage shall not be longer than m.)