Increment array by plus one

class Solution {
public:
    vector<int> plusOne(vector<int>& digits) {
        int n = digits.size();
        if(digits[n-1] != 9){
            digits[n-1] = digits[n-1] + 1;
            return digits;
        }
        int i = n-1;
        while(digits[i] == 9){
            
            // But if all the digits are 9. Then make the 1st digit 1 and then push 0 at the end.
            if(i == 0){
                digits[i] = 1;
                digits.push_back(0);
                return digits;
            }
            digits[i] = 0;
            i--;   
        }
        
        digits[i] = digits[i] + 1;
        return digits;
    }
};