Seal the Registry

Registry keeps a mutable index but exposes it safely. Implement in Solution: - static class Registry with put(String k, int v), int get(String k) (missing → throw NoSuchElementException), Map<String, Integer> snapshot() (unmodifiable view), and Map<String, Integer> frozenCopy() (independent immutable copy). - static int totalOf(Map<String, Integer> values) summing the values — it must compile against either of the two exposure styles. The test mutates the registry after taking a snapshot to prove the copy stays independent.

Difficulty: intermediate