> For the complete documentation index, see [llms.txt](https://maksimdan.gitbook.io/interview-practice-problems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://maksimdan.gitbook.io/interview-practice-problems/leetcode_sessions/66-plus-one.md).

# 66 Plus One

Given a non-negative number represented as an array of digits, plus one to the number.

The digits are stored such that the most significant digit is at the head of the list.

```cpp
vector<int> plusOne(vector<int>& digits) 
{
    int end = digits.size() - 1;
    while (end >= 0 && digits[end] == 9) {
        digits[end--] = 0;
    }
    if (end == -1) {
        digits.insert(digits.begin(), 1);
        return digits;
    }
    digits[end]++;
    return digits;
}

int main()
{
    vector<int> test = { 1,2,3,4,5,6,7,8 };
    print(plusOne(test));

    vector<int> test2 = { 1,9,9,9 };
    print(plusOne(test2));

    vector<int> test3 = { 9,9,9,9 };
    print(plusOne(test3));
}
```