0066. Plus One

"""You are given a large integer represented as an integer array digits, where each digits[i] is the ith digit of the integer. 
The digits are ordered from most significant to least significant in left-to-right order. 
The large integer does not contain any leading 0's.
Increment the large integer by one and return the resulting array of digits.

Input: digits = [4,3,2,1]
Output: [4,3,2,2]

Input: digits = [9]
Output: [1,0]
"""

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
          n = len(digits)
          for i in range(n):
                idx = n - 1 - i #visit from end
                if digits[idx] == 9:
                    digits[idx] = 0
                else   : 
                     digits  [idx] += 1
                     return digits
          return [1] + digits