> Very useful pattern but I don't believe it has a name.

This is an instance of “use the right data structure for the job”. To me it has little to do with architectural design (where design patterns live), but it has to do with algorithmic design.

This is the thrust of much of the excellent "Algorithm Design Manual" by Skiena -- choosing the right data structure to model your problem can take you 95% of the way toward the best solution.