说明：  一个给定的S={a1,a2,a3,…,an},若有P={a_x1,a_x2,a_x3,…,a_xm},满足(x1 < x2 < … < xm)且( ax1 < ax2 < … < axm),就称P 为S 的一个上升序列。如果有多个P 满足条件，那么 我们想求字典序最小的。
(A given S = {a1, a2, a3, ..., an}, if P = {a_x1, a_x2, a_x3, ..., a_xm}, satisfy (x1 < x2 < ... < xm) and (ax1 < ax2 < ... < axm), called P S in a rising sequence. If you have multiple P satisfy the condition, then we would like to seek the lexicographical smallest.)