LC66. Plus One

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
        carry = 1
        for i, d in enumerate(digits[::-1]):
            digits[len(digits) - i - 1] = (d + carry) % 10
            carry = 1 if d + carry == 10 else 0
 
        if carry == 1:
            return [1] + digits
        
        return digits

Complexity

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