问题
Having a sorted dict (hash table, map or whatever key/value structure) you can easily have a binary search to look for an item. If we assume the keys are unique but values could be repeated, what data structure can we use to have O(log n) retrieval for keys and also O(log n) query to find count of values=something in the given data?
回答1:
Two binary search trees, one for keys, second for values, with mutual pointers will provide the required functionality. The pointers can be many-to-one from keys to values and one-to-many from values to keys.
来源：https://stackoverflow.com/questions/29356948/what-data-structure-to-use-to-have-olog-n-key-and-value-lookup