C# - Replace Every Second Space, But Not First/last With " " In A Given String?

let's say I have the following string:

string s = "A B C D TESTTEST BLA BLA TEST TEST2"

Then I need the following:

"A B C D TESTTEST BLA BLA TEST TEST2"

So the rules are:a) replace every second space (between non space chars) with

b) If the last space is replaced with , try to move it backwards (if possible) one step so the next word is not touched by the force space.

Background:I want to use that to print data from the database to my website. But I want to optimize the forced spaces to use less space. I also want the last forced space not to touch the next word (if possible) so it is easier for some search engines to catch that word.

Will I need to loop through every char in that string and count the occurrence or is there an easier, faster and more fancy way?]So I did a benchmark to figure out which solution to accept:

@Guffa, your solution needs 22 seconds for 1 Million runs
@Timwi, your solution needs 7 seconds for 1 Million runs

I will give you both an upvote, but I will accept Timwi's solution.