Catenyms

Catenyms

时间： 1ms        内存：128M

描述：

A catenym is a pair of words separated by a period such that the last letter of the first word is the same as the last letter of the second. For example, the following are catenyms:

dog.gopher
gopher.rat
rat.tiger
aloha.aloha
arachnid.dog

A compound catenym is a sequence of three or more words separated by periods such that each adjacent pair of words forms a catenym. For example,

aloha.aloha.arachnid.dog.gopher.rat.tiger

Given a dictionary of lower case words, you are to find a compound catenym that contains each of the words exactly once. The first line of standard input contains

t

, the number of test cases. Each test case begins with 3 <=

n

<= 1000 - the number of words in the dictionary.

n

distinct dictionary words follow; each word is a string of between 1 and 20 lowercase letters on a line by itself. For each test case, output a line giving the lexicographically least compound catenym that contains each dictionary word exactly once. Output "***" if there is no solution.

输入：

输出：

示例输入：

2
6
aloha
arachnid
dog
gopher
rat
tiger
3
oak
maple
elm

示例输出：

aloha.arachnid.dog.gopher.rat.tiger
***

提示：

参考答案：

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