【LeetCode】Plus One (2 solutions)

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.

从个位数字往前扫，只要一个数字不为9，即可加1返回。

如果直到最高位仍为9，则说明结果为100…0

解法一：

可能会使用额外空间与复制数组

class Solution {
public:
    vector<int> plusOne(vector<int> &digits) {
        for(int i = digits.size()-1; i >= 0; i --)
        {
            if(digits[i] <= 8)
            {
                digits[i] += 1;
                return digits;
            }
            else
            {//9
                if(i != 0)
                    digits[i] = 0;
                else
                {
                    vector<int> result(1,1);
                    result.push_back(0);
                    for(int j = 1; j < digits.size(); j ++)
                        result.push_back(digits[j]);
                    return result;
                }
            }
        }
    }
};

解法二：

inplace且不用复制数组

class Solution {
public:
    vector<int> plusOne(vector<int> &digits) {
        for(int i = digits.size()-1; i >= 0; i --)
        {
            if(digits[i] <= 8)
            {
                digits[i] += 1;
                return digits;
            }
            else
            {//9
                if(i != 0)
                    digits[i] = 0;
                else
                {
                    digits[0] = 1;
                    digits.push_back(0);
                    return digits;
                }
            }
        }
    }
};