2025-12-26 21:12:54 +0300 MSK

class CombinationIterator:

    def __init__(self, characters: str, combinationLength: int):
        self._length: int = combinationLength
        self._chars: str = characters
        self._cur: list[str] = []
        self._gen = self._generator(0)
        self._nxt: Optional[str] = next(self._gen, None)
    
    def _generator(self, i: int) -> Generator[str, None, None]:
        if len(self._cur) == self._length:
            yield "".join(self._cur)
            return
        if i >= len(self._chars):
            return
        char = self._chars[i]
        self._cur.append(char)
        yield from self._generator(i + 1)
        self._cur.pop()
        yield from self._generator(i + 1)

    def next(self) -> str:
        nxt = self._nxt
        self._nxt = next(self._gen, None)
        return nxt

    def hasNext(self) -> bool:
        return self._nxt is not  None


# Your CombinationIterator object will be instantiated and called as such:
# obj = CombinationIterator(characters, combinationLength)
# param_1 = obj.next()
# param_2 = obj.hasNext()