from __future__ import annotations from mountain import Mountain class MountainManager: def __init__(self) -> None: pass def add_mountain(self, mountain: Mountain) -> None: raise NotImplementedError() def remove_mountain(self, mountain: Mountain) -> None: raise NotImplementedError() def edit_mountain(self, old: Mountain, new: Mountain) -> None: raise NotImplementedError() def mountains_with_difficulty(self, diff: int) -> list[Mountain]: raise NotImplementedError() def group_by_difficulty(self) -> list[list[Mountain]]: raise NotImplementedError()