Unique Goodies Sets

You are given a set of goodies and a positive integer n. Your task is to generate all unique combinations (or sets) of goodies such that each combination contains exactly n items. The combinations must be derived from the sorted order of the goodies (i.e. lexicographical order) and output one combination per line with the items separated by a single space.

More formally, given an integer \( n \) and a list of strings, first sort the list in lexicographical order; then, output every combination of \( n \) distinct goodies. If no such combination exists (for example, when the list is empty), output nothing.

Note: Sorting is performed using the default lexicographical order.

inputFormat

The input is read from standard input and has the following format:

<n>
<k>
item1
item2
... 
itemk

where:

• n is the number of items each combination should contain.
• k is the number of available goodies.
• Each of the following k lines contains a non-empty string representing a goodie.

outputFormat

Output all unique combinations of n goodies computed from the sorted list. Each combination should be printed on a separate line, with the goodies separated by a single space. If no combination exists, output nothing.

## sample

2
4
pen
notebook
mug
sticker

mug notebook
mug pen
mug sticker
notebook pen
notebook sticker
pen sticker

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