Just completed some tests on both versions (cased and if elsed) for 10,000,000 iterations ifed took on average 3745820 ticks and cased for same tests took on average 3565270 ticks so realy is no diference. I think you are right Voile :) I have to aggre whit you this time :)

Yep I think this one is best

:)

And Arphox I think your solution is not that good to :) string builder is good choise only if strings are big or is many of them like milion or so. In this case Concat or string join something like this or even aggregate is better choise when building small string.

Yes this solution is not the best performance wise its jus simple one :)

In some cases Linq performance is good in some it is slower. In this case concat & case is good choise. If strings would be massive or many of them then string builder would be better choise.

Yes Case method for performance best in this case

It's not a duplicate as it is in c#.

I agree whit BNoohi. But your (BNoohi) solution is not the best to if youl pass something like "2 4 10 8 7" your solution wil trow an out of range exception :)

Voile "As mentioned by lechevalier below, you need to get rid of a certain division ;-)"
You mean replace division to another method like multiply & shift ? Or I'm looking to wrong direction?

I been thinking to do division on first part where numbers still small but then Im geting floating point and in this case I can't do multiplications using biginteger. I need sit down and rethink twist that formula :)