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### leetcode Insert Delete GetRandom O(1)

Design a data structure that supports all following operations in O(1) time.

1. insert(val): Inserts an item val to the set if not already present.
2. remove(val): Removes an item val from the set if present.
3. getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.

Example:

ps ：无聊身边没电脑用手机1A了此题。。。还发了blog