How does this account for string casing, i.e uppercase, lowercase?

OP's solution is better imo. More readable, and doesn't add clutter (Not that yours does)

Haha I like that

Why does using regex make it slow?

But it's slower

How about mine? What's the time and space complexity

Still too much. My solution is just as readable (if not more so) and has way less code. I'm open to see better ones but this ain't it imo

Very nice. I wonder if it's the most efficient in Big O

But you defined new variables yourself

Wouldn't let me

Kata says there should be a default parameter...

Either I'm stupid or this kata is frustratingly contradictory

The uppercase and lowercase together! I swear the way some people think... brilliant

You can remove the quotation marks