Apologies, maybe I oversimplified the original problem. I'm dealing with IP's (both v4 and v6), subnets, ranges (which may or may not align to subnets). These map to one or more datacenter numbers.

I could indeed define data model, parse the data thoroughly, optimize in-memory data structure, and so on. That requires rigid data structure, knowing access pattern and understanding the problem space. I'm not there yet. Instead, I created this generic tool which works with any text files, and fell into a rabbit hole of over-optimizing it. That's it.