Implement a Snapshot Set Iterator

Design and implement a set data structure that supports snapshot iteration. The set stores unique values. It must support the following operations: - `add(value)`: Add `value` to the set if it is not already present. - `remove(value)`: Remove `value` from the set if it is present. If it is absent, do nothing. - `contains(value) -> bool`: Return whether `value` is currently in the set. - `iterator()`: Return an iterator over a snapshot of the set at the moment the iterator is created. Snapshot iterator requirements: - The iterator should return exactly the values that were present in the set when the iterator was created. - Later calls to `add` or `remove` must not affect already-created iterators. - The return order of values is not important. - Each value in the snapshot should be returned exactly once. Example: ```text s = SnapshotSet() s.add(1) s.add(2) it = s.iterator() s.remove(1) s.add(3) # The iterator should still return 1 and 2 in any order. # It should not return 3. ``` Implement the data structure and iterator. Discuss the time and space complexity of your approach.