题目要求的是求每组字符串中最长子串的长度。 简单的搜索入门题，也是很好的字符串题，包含了求反串，求子串，字符串查找，求字符串长度。

You are given a number of case-sensitive strings of alphabetic characters, find the largest string X, such that either X, or its inverse can be found as a substring of any of the given strings.

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以后你们还会学到更多，你会学到字符串，不仅仅能运用标准数值运算，你还可以对他们求长度，或者加上其他的东西。

You're going to get a chance to explore them, and you'll see not only are there the standard numerics for strings, there are things like length or plus or other things you can do with them.

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