Your solution inspired me to learn more about Regex.
Well done.

there's no need to check n equal 5, 7 & 11 in 2nd if. As it's already covered in for loop iterations.

very effective solution)

Very nice solution!

leverage that sig is changing right?

cool! match vs split

This is harmony

This is the most unique and best solution. It's a pity that I could not think of this) Thanks

really neat

Since nobody has pointed it out yet: this is O(n^2), which is not great. Every time it runs replace it has to read in the entire string, and it has to do this an amount of times that is in worst-case proportionate to the entire string. For example, if my string is ['NORTH', 'WEST', 'NORTH', 'SOUTH', 'EAST', 'SOUTH'] or a similar construction, I can only remove one pair at a time. So for a string with N pairs, I have to read N times, and the lengths each time are (N), (N-1), (N-2), etc.

It is however clever as hell. Behold the power of regex.