Leetcode: Plus One

Problem Description

Problem definition is taken from leetcode.

• Plus One

Given a non-empty array of decimal digits representing a non-negative integer, increment one to the integer.

The digits are stored such that the most significant digit is at the head of the list, and each element in the array contains a single digit.

You may assume the integer does not contain any leading zero, except the number 0 itself.

Example 1

Input: digits = [1,2,3]
Output: [1,2,4]
Explanation: The array represents the integer 123.

Example 2

Input: digits = [4,3,2,1]
Output: [4,3,2,2]
Explanation: The array represents the integer 4321.

Solution

Space and time complexity is O(N)

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
        result = []
        carry = 0
        increment = 1
        for d in reversed(digits):
            d = d+carry+increment
            carry = 0
            increment = 0
            
            if d >= 10:
                carry = 1
                d = d - 10
            
            result.append(d)
        
        if carry == 1:
            result.append(1)
        
        return reversed(result)