vector<int> plusOne(vector<int>& digits) {
vector<int> res;
int carry = 1;
for (int i = digits.size() - 1; i >= 0; i--) {
int sum = carry + digits[i];
carry = sum / 10;
res.push_back(sum % 10);
}
if (carry) res.push_back(1);
reverse(res.begin(), res.end());
return res;
}