With 'attr_accessor' defined you can access the elements without '@'.

Thanks for the comment :)
I know it could have been done with one iteration with reduce, but this way mapping and summing are not wired together. Easier to read and until it does not cause performance issues I prefer these kind of solutions.
I use this pattern to introduce separation of conserns to my students as well :)

Using map and sum iterates 2 times in the String. With a reduce you can subsctract and accumulate.

Yes, totally.
We can do in O(n) if we first count the string chars and later do the check.

I did it, but I know about the performance.

Clean and easy to read solution. Regex doesnt pay off their cost.

But its less readable. Nice trade to discuss hahaha