Implement a Set with Readable Snapshots

Question

The question asks the candidate to implement a set data structure that supports creating snapshots of its state, allowing for retrieval of the set's contents at specific points in time.

Codemia · Accepted Answer

To implement a snapshot set, we need to support the following operations:
1. **Add**: Insert an element into the set.
2. **Remove**: Delete an element from the set.
3. **Create Snapshot**: Capture the current state of the set.
4. **Get Snapshot**: Retrieve the elements of the set as they were at the time of a specific snapshot.

The snapshot set can be implemented using a combination of a hash set to store the current elements and a list to maintain snapshots. Each snapshot will be a copy of the current state of the set at the time of the snapshot creation. This allows for efficient retrieval of the set's state at any given snapshot without affecting the current state.

Here is a basic implementation in Python:
```python
class SnapshotSet:
    def __init__(self):
        self.current_set = set()
        self.snapshots = []

def add(self, value):
        self.current_set.add(value)

def remove(self, value):
        self.current_set.discard(value)

def create_snapshot(self):
        snapshot = self.current_set.copy()
        self.snapshots.append(snapshot)
        return len(self.snapshots) - 1  # return snapshot index

def get_snapshot(self, index):
        if 0 <= index < len(self.snapshots):
            return self.snapshots[index]
        else:
            raise IndexError('Snapshot index out of range')
```
This implementation uses a set for current elements and a list for snapshots, ensuring that both operations are efficient.

One trade-off of this implementation is memory usage, as each snapshot is a complete copy of the current set. In scenarios with a large number of snapshots or a large set, this could lead to high memory consumption. To mitigate this, we could explore more efficient snapshotting techniques, such as using a copy-on-write strategy or only storing deltas between snapshots.

Implement a Set with Readable Snapshots

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