fast indexing for slow cpu?

fast indexing for slow cpu?

I have a large document that I want to build an index of for word
searching. (I hear this type of array is really called a concordances).
Currently it takes about 10 minutes. Is there a fast way to do it?
Currently I iterate through each paragraph and if I find a word I have not
encountered before, I add it too my word array, along with the paragraph
number in a subsidiary array, any time I encounter that same word again, I
add the paragraph number to the index. :
associativeArray={chocolate:[10,30,35,200,50001],parsnips:[5,500,100403]}
This takes forever, well, 5 minutes or so. I tried converting this array
to a string, but it is so large it won't work to include in a program
file, even after removing stop words, and would take a while to convert
back to an array anyway.
Is there a faster way to build a text index other than linear brute force?
I'm not looking for a product that will do the index for me, just the
fastest known algorithm. The index should be accurate, not fuzzy, and
there will be no need for partial searches.