this seems very O(n) to me. I think we should be doing this in O(logn)

The char datatype can be treated as its unicode equivalent without typecasting or converting. So it's is evaluating the chars based on their unicode equivalents. If you're not familiar with Unicode you definetly need to research it.

Wait im confused, this probably a dumb question but where do you access the alphabet in this?

As many top 'coding craftsman' already said, when your variable needs an explaining comment you did something wrong