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

`insert(val)`

: Inserts an item val to the set if not already present.`remove(val)`

: Removes an item val from the set if present.`getRandom`

: Returns a random element from current set of elements. Each element must have the**same probability**of being returned.

**Example:**

// Init an empty set. RandomizedSet randomSet = new RandomizedSet(); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomSet.insert(1); // Returns false as 2 does not exist in the set. randomSet.remove(2); // Inserts 2 to the set, returns true. Set now contains [1,2]. randomSet.insert(2); // getRandom should return either 1 or 2 randomly. randomSet.getRandom(); // Removes 1 from the set, returns true. Set now contains [2]. randomSet.remove(1); // 2 was already in the set, so return false. randomSet.insert(2); // Since 2 is the only number in the set, getRandom always return 2. randomSet.getRandom();

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