Leetcode: Plus One

Plus One | LeetCode OJ

1. Reverse Iterate through the array
2. As long as there are only 9’s convert them to one
3. For a non-9 number add 1 and break
4. Check if the first number is 0, indicating that all the numbers were 9, insert 1 at the beginning for this case

Remarks:

1. O(n) time, O(1) space

class Solution(object):
    def plusOne(self, digits):
        """
        :type digits: List[int]
        :rtype: List[int]
        """
        for i in range(len(digits) - 1, -1, -1):
            if digits[i] == 9:
                digits[i] = 0
            else:
                digits[i] += 1
                break
        if digits[0] == 0: digits.insert(0, 1)
        return digits

Traverse a list in reverse order in Python