hackercupai/hackercup huggingface dataset:
You've been given a list of words to study and memorize. Being a diligent
student of language and the arts, you've decided to not study them at all and
instead make up pointless games based on them. One game you've come up with is
to see how you can concatenate the words to generate the lexicographically
lowest possible string.

### Input

As input for playing this game you will receive a text file containing an
integer **N**, the number of word sets you need to play your game against.
This will be followed by **N** word sets, each starting with an integer **M**,
the number of words in the set, followed by **M** words. All tokens in the
input will be separated by some whitespace and, aside from **N** and **M**,
will consist entirely of lowercase letters.

### Output

Your submission should contain the lexicographically shortest strings for each
corresponding word set, one per line and in order.

### Constraints

1 ≤ **N** ≤ 100
1 ≤ **M** ≤ 9
1 ≤ all word lengths ≤ 10