What is a permuted index?

I have an exercise to do, but i don't understand what the question is asking me:

Design and impliment a program to produce a permuted index. A permuted index is one in which each phrase is indexed by every word in the phrase. So, given the following input,

Code:

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          The quick brown fox
          jumped over the fence

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the output would be

Code:

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              The quick      brown fox
      jumpted over the      fence
        The quick brown      fox
                              jumpted over the fence
                jumpted      over the fence
                    The      quick brown fox
          jumpted over      the fence
                              The quick brown fox

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I have no idea what the question is asking me, is a permuted index just a vector of strings, each string corresponding to a word in the phrase? If so, i fail to see how that relates to the output they want.

Thanks in advance.

A permutation is when you have a certain number of elements and arrange them in every combination possible.

ie:

Code:

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A B C would  be:

A B C
A C B
B A C
B C A
C A B
C B A

I'm not sure about this one, but I think it can contain
combinations which does not have every element in it too:

A
B
C
A B
B A
B C
C B
A C
C A

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I see, but in the example they give, the output doesn't seem to have every possible combination of the words given in the input.

I still don't quite see what they are asking me to do.