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2925.   Word Ladder
Time Limit: 1.0 Seconds   Memory Limit: 65536K
Total Runs: 420   Accepted Runs: 89

A word ladder is a sequence of words, in which two consecutive words differ by exactly one letter. An example of such a ladder (usually arranged vertically, hence the "ladder") would be: beer, brew, brow, word, down. Note that to get from one word to the next, the letters may be rearranged, and exactly one letter is changed.

For this problem, you will be given a dictionary of distinct words, all of the same length. Your task is to write a program that finds a word ladder of minimal length, such that the first and last word of the ladder have no letters in common.


On the first line an integer t (1 ≤ t ≤ 100): the number of test cases. Then for each test case:

  • A line with two space-separated integers n (2 ≤ n ≤ 100) and l (1 ≤ l ≤ 20): the number of words and their length.
  • n lines with a word, each consisting of l lowercase letters (a - z).


    For each testcase:

  • a single line with the words in a ladder of minimal length, separated by a single space.

    It is guaranteed that at least one such ladder can be constructed. If there is more than one, output the one that comes first lexicographically.

    Sample Input

    9 3

    Sample Output

    ale alt apt opt


    If s and t are strings of equal length and si denotes the i-th character of s, then s precedes t lexicographically if for some i: si < ti and sj = tj for all j < i.

  • Source: TJU Team Selection Contest 2008 (1)
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