Plus One

• Difficulty: Easy
• Primary pattern: Arrays & Strings
• Tags: Array, Math
• Time taken: 11:48
• LeetCode Link

Key Idea

• Trick here is knowing how to reverse the range()
• To rever range(5,-1,-1) means from 5 to -1 (not including -1) in reverse order

Solution

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
        # Inputs: List[int]
        # Outputs: List[int]
        # Description:
            # Increment "digits" by one and return the list
        # E.g. [1,2,3] reutrns [1,2,4]
        
        # Increment last by 1
        for i in range(len(digits) - 1, -1, -1):
            if digits[i] < 9:
                digits[i] += 1
                return digits
            digits[i] = 0
        return [1] + digits

Complexity

• Time: O(n)
• Space: O(1)