66. Plus One.py

"""
https://leetcode.com/problems/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.

Example 1:
    Input: digits = [1,2,3]
    Output: [1,2,4]
    Explanation: The array represents the integer 123.
    Incrementing by one gives 123 + 1 = 124.
    Thus, the result should be [1,2,4].

Example 2:
    Input: digits = [4,3,2,1]
    Output: [4,3,2,2]
    Explanation: The array represents the integer 4321.
    Incrementing by one gives 4321 + 1 = 4322.
    Thus, the result should be [4,3,2,2].

Example 3:
    Input: digits = [9]
    Output: [1,0]
    Explanation: The array represents the integer 9.
    Incrementing by one gives 9 + 1 = 10.
    Thus, the result should be [1,0].

"""


class Solution(object):
    def plusOne(self, digits: list):
        """
        :type digits: List[int]
        :rtype: List[int]

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

        """

        for i in range(len(digits) - 1, -1, -1):
            if digits[i] == 9:
                digits[i] = 0
            else:
                digits[i] += 1
                return digits

        return [1] + digits


solution = Solution()

assert solution.plusOne([1, 2, 3]) == [1, 2, 4]
assert solution.plusOne([4, 3, 2, 1]) == [4, 3, 2, 2]
assert solution.plusOne([9]) == [1, 0]
assert solution.plusOne([9, 9]) == [1, 0, 0]
assert solution.plusOne([1]) == [2]