plus-one.py

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
        if digits[-1] < 9:
            digits[-1] += 1
            return digits
        elif len(digits) == 1 and digits[0] == 9:
            return [1, 0]
        else:
            digits[-1] = 0
            digits[0:-1] = self.plusOne(digits[0:-1])
            return digits