Problem URL: Plus one

First we reverse the list, then add one to the fist item, if the number is 9, then we keep a carry and add it to the next number. We will do that until all the digit in the list have been iterated through. Then we return the reversed list.

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
        one = 1
        i = 0
        digits = digits[::-1]

        while one:
            if i < len(digits):
                if digits[i] == 9:
                    digits[i] = 0
                else:
                    digits[i] += 1
                    one = 0
            else:
                digits.append(one)
                one = 0
            i += 1

        return digits[::-1]

Time Complexity: O(n)
Space Complexity: O(1)