text: class Solution(object):
    def plusOne(self, digits):
      """
      :type digits: List[int]
      :rtype: List[int]
      """
      up = 1
      ind = len(digits) - 1
      while up == 1 and ind >= 0:
        digits[ind] += up
        up = digits[ind] // 10
        digits[ind] %= 10
        ind -= 1
      if up == 1:
        return [1] + digits
      else:
        return digits
  
  if __name__ == "__main__":
    sol = Solution()
    sol.plusOne([2,9,9])