66. Plus One

1. Description

You are given a large integer represented as an integer array digits, where each digits[i] is the $i^{th}$ digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0’s.
Increment the large integer by one and return the resulting array of digits.

2. Example

Example 1

Input: digits = [1,2,3]
Output: [1,2,4]
Explanation: The array represents the integer 123.
Incrementing by one gives 123 + 1 = 124.
Thus, the result should be [1,2,4].

Example 2

Input: digits = [4,3,2,1]
Output: [4,3,2,2]
Explanation: The array represents the integer 4321.
Incrementing by one gives 4321 + 1 = 4322.
Thus, the result should be [4,3,2,2].

Example 3

Input: digits = [9]
Output: [1,0]
Explanation: The array represents the integer 9.
Incrementing by one gives 9 + 1 = 10.
Thus, the result should be [1,0].

3. Constraints

• 1 <= digits.length <= 100
• 0 <= digits[i] <= 9
• digits does not contain any leading 0’s.

4. Solutions

Array

n = digits.size()
Time complexity : O(n)
Space complexity : O(1)

class Solution {
public:
    vector<int> plusOne(vector<int> digits) {
        const int n = digits.size();
        for (int i = n - 1; i >= 0; --i) {
            if (digits[i] < 9) {
                ++digits[i];

                return digits;
            } else {
                digits[i] = 0;
            }
        }

        digits.insert(digits.begin(), 1);

        return digits;
    }
};