LeetCode 66. Plus One

class Solution {
public:
    vector<int> plusOne(vector<int>& digits) {
        if (digits[digits.size() - 1] != 9) {
            digits[digits.size() - 1]++;
            return digits;
        }
        
        int carry = 1;
        for (int i = digits.size() - 1; i >= 0; i--) {
            digits[i] += carry;
            carry = digits[i] / 10;
            digits[i] = digits[i] % 10;
        }
        
        if (carry != 0) {
            digits.insert(digits.begin(), carry);
        }
        
        return digits;
    }
};