How can I permute pairs across a set?

Posted by sila on Programmers See other posts from Programmers or by sila
Published on 2011-11-19T08:52:57Z Indexed on 2011/11/19 18:14 UTC
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algorithms

I am writing a bet settling app in C# and WinForms. I have 6 selections, 4 of them have won. I know that using the following formula from Excel:

=FACT(selections)/(FACT(selections-doubles))/FACT(doubles)

This is coded into my app and working well: I can work out how many possible doubles (e.g., AB, AC, AD, AE, BC, BD, BE, etc.) need to be resolved.

But what I can't figure out is how to do the actual calculation. How can I efficiently code it so that every combination of A, B, C, and D has been calculated?

All my efforts thus far on paper have proved to be ugly and verbose: is there an elegant solution to this problem?

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