[LintCode] Plus One 加一运算

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.

Have you met this question in a real interview? 

Yes

Example

Given [1,2,3] which represents 123, return[1,2,4].

Given [9,9,9] which represents 999, return[1,0,0,0].

LeetCode上的原题，请参见我之前的博客Plus One。

解法一：

class Solution {
public:
    /**
     * @param digits a number represented as an array of digits
     * @return the result
     */
    vector<int> plusOne(vector<int>& digits) {
        vector<int> res;
        int carry = 1, n = digits.size();
        for (int i = n - 1; i >= 0; --i) {
            int sum = digits[i] + carry;
            res.insert(res.begin(), sum % 10);
            carry = sum / 10;
        }
        if (carry == 1) res.insert(res.begin(), 1);
        return res;
    }
};

解法二：

class Solution {
public:
    /**
     * @param digits a number represented as an array of digits
     * @return the result
     */
    vector<int> plusOne(vector<int>& digits) {
        for (int i = digits.size() - 1; i >= 0; --i) {
            if (digits[i] < 9) {
                digits[i] += 1;
                return digits;
            }
            digits[i] = 0;
        }
        digits.insert(digits.begin(), 1);
        return digits;
    }
};