Thank you!! That's pretty handy :)

you needn't use an if block for the return values, it would make your code more compact without sacrificing readability to simply return the condition, which itself is a boolean.

Yes, using Counter like you did is better. Or counting yourself with a dict and a single pass through the array.

Wouldn't this end up having quadratic (worst case) complexity? You'll traverse all of s at least s times?