Multiply Strings(字符串乘法模拟，包含了加法模拟)

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note: The numbers can be arbitrarily large and are non-negative.

要求：字符串表示的数字可能无穷大，并且非负。

class Solution {
private:
    vector<string> tempStrs;
public:
    string add(string num1,string num2)
    {
        int n1=num1.size();
        int n2=num2.size();
        int i=n1-1;int j=n2-1;
        string resStr;
        int jinwei=0;
        while (i>=0&&j>=0)
        {
            int temp=(num1[i]-'0')+(num2[j]-'0')+jinwei;
            jinwei=temp>=10?1:0;
            temp%=10;
            resStr.push_back(temp+'0');
            --i;
            --j;
        }
        if(i>=0){
            while (i>=0)
            {
                int temp=(num1[i]-'0')+jinwei;
                jinwei=temp>=10?1:0;
                temp%=10;
                resStr.push_back(temp+'0');
                --i;
            }
        }
        else if(j>=0){
            while (j>=0)
            {
                int temp=(num2[j]-'0')+jinwei;
                jinwei=temp>=10?1:0;
                temp%=10;
                resStr.push_back(temp+'0');
                --j;
            }
        }
        if(jinwei!=0){
            resStr.push_back(jinwei+'0');
        }
        reverse(resStr.begin(),resStr.end());
        return resStr;
    }
    string multiply(string num1, string num2) {
        if(num1.empty()||num2.empty()) return "";
        if(num1=="0"||num2=="0") return "0";
        int jinwei=0;
        int n1=num1.size();
        int n2=num2.size();
        if(n2>n1){
            string temp=num1;
            num1=num2;
            num2=temp;
            n1=num1.size();
            n2=num2.size();
        }
        int time=0;
        string tempStr;
        string res;
        for(int i=n2-1;i>=0;--i)
        {
            tempStr.clear();
            jinwei=0;
            for(int j=n1-1;j>=0;--j)
            {
                int temp=(num1[j]-'0')*(num2[i]-'0')+jinwei;
                jinwei=temp>=10?(temp/10):0;
                temp=temp%10;
                tempStr.push_back(temp+'0');
            }
            if(jinwei!=0){
                tempStr.push_back(jinwei+'0');
            }
            reverse(tempStr.begin(),tempStr.end());
            for(int q=0;q<time;++q){
                tempStr.push_back('0');
            }
            tempStrs.push_back(tempStr);
            ++time;
        }
         if(tempStrs.size()>1){
            res=add(tempStrs[0],tempStrs[1]);
            for (int i=2;i<tempStrs.size();++i)
            {
                res=add(res,tempStrs[i]);
            }
            return res;
        }else
        {
            return tempStrs[0];
        }

    }
};