Design a multiset that allows duplicate values and supports these operations in average constant time: insert(val), remove(val), and getRandom(). To make the problem deterministic for testing, you are given a list of operations to process. Rules: - ('insert', val): insert one occurrence of val. Return True if val was not already present in the multiset before this insertion, otherwise return False. - ('remove', val): remove one occurrence of val. If multiple active occurrences exist, remove the most recently inserted active occurrence of val. Return True if an occurrence was removed, otherwise False. - ('getRandom', r): if the multiset currently contains n occurrences, return the value stored at index (r % n) of the internal active array used by your design. The active array must support O(1) average insertion and deletion via swap-with-last. If the multiset is empty, return None. Return the result of every operation in order.