题目：



Given two non-negative integers ​​num1​​ and ​​num2​​ represented as string, return the sum of ​​num1​​ and ​​num2​​.

Note:

  1. The length of both 

​​num1​​

  1.  and 

​​num2​​

  1. Both 

​​num1​​

  1.  and 

​​num2​​

  1.  contains only digits 

​​0-9​​

  1. .
  2. Both 

​​num1​​

  1.  and 

​​num2​​

  1. You must not use any built-in BigInteger library or convert the inputs to integer

思路：

本题本质上十进制加法运算，满十进1，题目无非将数值转换成字符串，可以各位减‘0‘求得大小

代码：

class Solution {
public:
    string addStrings(string num1, string num2) {
        int i =num1.size()-1,j=num2.size()-1;
        int carry = 0;
        string res ="";
        while(i>=0||j>=0||carry)
        {
            int sum = 0;
            sum +=carry;
            if(i>=0)
            {
                sum += (num1[i] - '0');
                i--;
            }
            if(j>=0)
            {
                sum+=(num2[j] - '0');
                j--;
            }           
            carry = sum / 10;
            sum = sum % 10;
            res += to_string(sum);                  
        }
        reverse(res.begin(),res.end());
        return res;
    }
};