Question：

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.

加1得新的数组

Algorithm：

从后往前遍历，遇9则变0，否则自加1。

Accepted Code：

class Solution {
public:
    vector<int> plusOne(vector<int>& digits) {
        int length = digits.size();
        for(int i=length-1;i>=0;i--)
        {
            if(digits[i] == 9)
                digits[i] = 0;
            else
            {
                digits[i]++;
                return digits;
            }
        }
        digits[0] = 1;
        digits.push_back(0);
        return digits;
    }
};