[LeetCode] Plus one

Problem: 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:

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

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

Input: digits = [0]
Output: [1]

Approach: It's an easy problem to solve. You can understand the approach by just looking at the implementation.

Implementation in C#:

        public static int[] PlusOne(int[] digits)

        {

            if (digits?.Length == 0)

            {

                return new int[0];

            }

            int n = digits.Length;

            for (int i = n - 1; i >= 0; --i)

            {

                if (digits[i] == 9)

                {

                    digits[i] = 0;

                }

                else

                {

                    ++digits[i];

                    return digits;

                }

            }

            // This is the case when all the digits are 9.

            digits = new int[n + 1];

            digits[0] = 1;

            return digits;

        }

Complexity: O(n)