题目描述：
LeetCode 380. Insert Delete GetRandom O(1)
Design a data structure that supports all following operations in O(1) time.
insert(val): Inserts an item val to the set if not already present.remove(val): Removes an item val ...
LeetCode 380. Insert Delete GetRandom O(1)
Design a data structure that supports all following operations in O(1) time.
insert(val): Inserts an item val to the set if not already present.remove(val): Removes an item val ...