Описание тега skip-lists
A skip list is a probabilistic data structure for storing and retrieving sorted data.
A skip list is a data structure comprised of multiple sorted linked lists, each of which has successively more elements than the last. The last list has all of the elements in the set being searched. Searches can be performed on this data structure by searching the sparsest level first, and moving to a deeper level only when two elements are found on the current level, one of which is above and one of which is below the desired value.
More info: https://en.wikipedia.org/wiki/Skip_list