cf----2019-09-16（WOW Factor，Tokitsukaze and Duel，Nick and Array）

明若清溪天下絕歌 繾綣成說，不知該在哪處着墨；一輩子情深怎奈何世事 徒留斑駁，只一念癡戀成奢。 Recall that string aa is a subsequence of a string bb if aa can be obtained from bb by deletion of several (possibly zero or all) characters. For exampl

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