260. Insert Delete GetRandom O(1)

Implement the RandomizedSet class with the following methods:
• insert(val): Inserts an item into the set. Returns true if not present, false otherwise.
• remove(val): Removes an item from the set. Returns true if present, false otherwise.
• getRandom(): Returns a random element. Each element has equal probability.

All operations should run in O(1) average time. For this problem, return the size of the set after a sequence of operations.

Example:
Input: ["insert", "remove", "insert", "getRandom", "remove"], [[1], [2], [2], [], [1]]
Output: 1 (final set size)

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