A DESCRIPTION OF THE PROBLEM :
SkipList is a commonly used data structure while it's not supported in Java. We only have ConcurrentSkipListMap, but it's used for different purposes, for: 1. it's used for concurrency, 2. it doesn't have a function for ranking. When I want to implement a function of ranking list, I can only refer to ZRANK in Redis. I suggest a similar implementation of SkipList or SkipListMap in Java to make such a process much easier.